When I was a kid (back in the 1960's) I always used a level line with my white Shakespeare fiberglass Wonderods. One reason was because the level lines were cheaper than the DT and WF lines, and by a lot. I just could not afford the tapered lines. Now, as an adult, I have gone back to level lines. I fish mostly in the small streams in The Great Smoky Mountains National Park. I fish mostly nymphs. A delicate presentation is not necessary as the line and leader is just flipped out a short ways upstream. The level line works perfectly for this. I'm not sure if level lines are even available in the stores anymore, but I have bought lots of them, NOS (brand new, never used) off of our favorite auction site for just a few dollars. I prefer the Scientific Anglers Air Cell level lines. What's not to like; good quality, very inexpensive, readily available, and they work.
Joe

Sure. Especially for panfish and bass, but with the right leader design (a stiffer first section than typical for a DT or WF of the same weight) can be fine for a lot of fishing.
Check some previous discussion, too: viewtopic.php?f=2&t=64497&p=335981&hilit=streak+of+outliers#p335981

Really the taper is only important in dry fly fishing , I think.
The taper dissipates line speed and energy rapidly so that the light weight dries will land without disturbance on the water. When I fish bass, I want disturbance, when I fish wets, nymphs, or streamers high speed at the tippet helps drive the fly down, an advantage to the level line. That higher tippet speed is also advantageous in turning over large or bulky flies.
On sinking lines a taper lets the line end sink less slowly than the line body causing the line to have a down sag and the fly to stay above the bottom, again an advantage to level lines.
So much of fly fishing lore has been about dry flies that we tend to think all flies should have the same tackle requirements that those Catskill flies needed. Many anglers still think that only dry fly fishing is "fly fishing", I've always been a "fly rod fisher" and have no qualms about using any fly, lure or bait with a fly rod. Yes I use level lines, sometimes. And, for those times when a taper is needed adding a yard or two of heavier leader butt as Whrlpool said will work just fine, I'd probably step up two steps from my normal butt, to maybe 0.024"

I have never used one but I am going to do that this year.I have recently purchased 5,6 and seven weight level lines off of ebay.I basically just fish ponds so it should be interesting.

If you look at their tapers online, many of the “aggressive” rocket/nymph/shooting lines aren’t too far from 30’ to 40’ of level line connected to a thinner running line. The difference, of course, is that you pay $80, or $100, or $130 for the fancy line and get a 5’ taper at the front. Seems like you could buy a couple of level lines and make them into aggressive taper lines for a lot less…

Well, several euro-nymphing lines are level if I'm not mistaken? Or why not just use mono for nymphing?

Very eye opening for me.I am self taught from books magazines VHS tapes and now web sites.Much of the vast amount of things i have read/watched is for stream fishing for trout.Not so much these days but when i started it all seemed much more complicated than it is.Always heard graphite was best.Weight forward lines were best.Never used DT until i went back to glass.I have fished since early chilhood and am a good multi species angler.I started fly fishing on and off 25 years ago but really got into it 10 years ago.ALWAYS was told level line is obselete and no one uses it.I have learned everything by myself.Except for my son on occasion i have never fly fished with another person.I rarely fish by any method with any one but the grand kids and sometimes my wife will grudgingly come along.How do you know the weight of a level line.I have several even a silk line or two.Until i joined here i always just used whatever decent quality WF according to what the rod said.Until i started going up and down with line weights etc I thought of many fine rods as defective or that i just would never cast decently.

If we look at 444 Peach in WF (https://www.cortlandline.com/collection ... 44-classic) it has 8' of front taper, 20' of level line (body) and 4' of rear taper followed by 58' of level running line.
444 Peach DT (https://www.cortlandline.com/products/4 ... r-fly-line) has the same 8' of front taper, 74' of level line (body or running line?) and 8' of rear taper which can become front taper.

Many of the modern "aggressive tapers" are rather like reversed Triangle Tapers up to a few feet from the tip and then rapidly tapered down to leader size; this reverse triangle means the line speed is increasing towards the tip right up until the front taper begins quickly dissipating all that energy, meaning the leader butt needs to be thicker and the leader must be longer or taper faster. The higher line speed does facilitate tighter loops and positive leader turnover. I believe level sections of lines tend to hold about the same speed throughout the length of the cast, perhaps requiring a bit more energy input, but I'm not a physicist, so I can't do the math to prove that.

@the hersh "How do you know the weight of a level line.I have several even a silk line or two"
In modern plastic lines the first thirty feet will weigh the same as that 30' of any AFTMA standard line, for example 30' #8=210g, 30' #6=160g, 30' #5=140g and because there is no reduced weight over that 30' for taper the next 30' will have the same mass, while a long belly WF or DT will be slightly heavier over the second 30'
In your silk of other braided lines the lines were manufactured and sold by diameter in inches and the weights are only approximately what AFTMA lines weigh. But we can say that "A" (0.060") ~#9 "B" (0.055")~#8 "C" (0.050")~#7 ect.
I use a $12 Harbor Freight gram scale to weigh a measured 30'. But the line weights are so close in 30' mass difference between AFTMA numbers, that about 5' more line out is like going up a line weight in the effect it has on the rod.

Front taper affects turnover and therefor presentation. You can always use a level line and put the taper in the leader (if you tie your own leaders). No question that especially for dry fly fishing, tapered lines and knotless tapered leaders are a convenience. I also think balanced, tapered lines and knotless tapered leaders are helpful for beginner casters. Also no question that tapered lines generate a lot of extra profit for line manufacturers.

When I was a kid, bargain fly outfits came with a level line.

As the front taper loses mass rapidly the loss of mass causes the fly to decelerate and that deceleration allows for a 'soft' presentation. A longer line taper or longer leader uses/loses more energy allowing softer delivery. I think that ideally for dry fly fishing the system runs completely out of energy just as the leader unfurls over the target and the fly settles onto the water without a ripple.
However if we are trying to sink a nymph or wet fly using something like a tuck cast, having lots of energy left at the end of the cast is what drives the fly deep, a splash at the entry seems desirable as that means the fly is going down quickly, in that case the energy lost to long leader or to line taper is detrimental to the desired presentation, I think. I get unweighted flies pretty near the bottom of a run by casting up stream with a hard entry, the hard high speed entry forces the fly through the surface tension and the current aids it in sinking as it moves back towards me on what becomes a 'slack' line.
I also like a splashy entry when using terrestrials, and again this can be accomplished by shortening leader or line taper to that a good bit of energy is still active at delivery.
As the Brits say "horses for courses".
Another use of level floating line that I've seen but haven't really used is a form of "indicator" or suspension nymphing; 15-20 years ago, I watched an old guy in the trout park catch fish for couple of seasons this way, he fixed a loop on the end of a level #6 line and then used 4# nylon mono loop-connected to that and varied the length of the mono to achieve the desired depth of travel, usually about 3-4' to his weighted fly. The floating line then became his "indicator" and "suspension device", the mono his tippet. His explanation was that the "bobber" used by most people countered any line or leader taper and that the result was the same exact rig he had - indicator-tippet-fly - complicated by unnecessary and expensive line taper and extruded leader, his line replaced the bobber and with his tippet tied directly to it, his rig was simple and effective.