DT lines do enable better control of the cast, the drift, or any other manipulations of the fly like swimming it, swinging, and so on. A better term might be "effective presentation," as opposed to "delicate" which usually implies emphasis on the way the fly lands. Still measuring a 50 foot cast to an exact landing spot and delicate placement is easier with a DT than a WF. Their advanatages aren't limited to dry fly presentations. Whenever it is an advantage to be in precise control of where the fly goes and what it does in the range of normal fishing distances, they have an edge. A WF line, not a specialy WF but a conventional one of the basic design of the fiberglass era, mutes that point to the distance where the running line enters the hand. Fishing to or across complex currents past that point when the running line is extended past the rod tip, control of the fly from the rod tip is compromised, except in dead straight retrieves across or up uniform currents. All less significant on still water or when the edge needs to go to distance or casting bulky/heavy flies relative to the line weight.