I am a believer in comp'ed sink lines, especially in currents and rocky drop offs. In currents, often the tapered end / leader rides higher than the belly of the sink line giving a false impression of the working depth. Having the front bite deeper helps a lot whether fishing for steelhead in a fast deep run -or- stripers in a tide rip. Also with rocky deep drops I hate how working the fly to a good depth gets the belly into the danger zone in sharp barnacle encrusted rocks as you strip the fly home. Density comp'ed (also called uniform sink) lines are much easier to keep out of the rocks for those times when you are thinking about where the fly is not the belly of the line.
Unfortunately I havent seen them in the compact head configurations (QD, Deep Sea, depth Charge, etc)... anyone else?