Some solo acoustic fingerstyle pieces I have written are in Dropped D for tonal purposes. I have one song in A Major, for example. The bassline is A, F#, D, E for the first part, and D, E, F#, F# for the second. It sounds great to descend from the A down to the E on bottom string, but if I don't play in dropped D, I have to play A down to F# up a minor sixth D, then down nearly a minor seventh to E. Those huge jumps in the bassline don't sound good, and if I opted to go from the A up to FX then descend to the D, it would be so high that it wouldn't even sound like a bassline. This is solo guitar, I don't have a bass player covering me! Catching that low D is crucial for the overall mood of the song. Also, the ascending D, E, F# bassline couldn't be achieved without drop D.

I also play some riffs where the drop D is helpful. For example, try playing this without drop D.

(pretty fast, in B Minor, cut and paste into Notepad)
E|----------------------------------------------|
B|----------------------------------------------|
G|----------------------------------------------|
D|-9-99-12p9-9-7-77-11p7-7-5-55-9p5-5-4-44-777--|
A|-9-99-9----9-7-77-7----7-5-55-5---5-4-44-777--|
D|-9-99-9----9-7-77-7----7-5-55-5---5-4-44-777--|

The powerchords themselves are easy to get, but reaching up to the third of each chord and pulling off is impossible in standard position (for me at least) unless you shift positions and stop playing the root for a beat (i.e.-playing the fifth and octave with your index and reaching up to the third with your pinky). In drop D you can play the riff without leaving out any notes or shifting positions mid-chord.

I think Drop D Tuning is kind of like guns... the invention itself is great. It's only bad in the wrong hands.

AND REMEMBER!!! Guns don't kill people... Bullets kill people!!