Emulating Other Instruments on Guitar
While recording with some friends the other day, a fellow guitarist was playing a melody completely on one string. It was a simple melody with just an octave range. Watching him do this, I remembered a point made by Fred Hamilton, the guitar professor at University of North Texas where he explained how playing a phrase on one string emulates the single column of air in a wind instrument. Listening to my friend play these melodies, it's easy to understand the concept.
Each string on the guitar has a different thickness, a different tension, and will react differently when plucked. By staying on one string and moving vertically, the only attribute you're changing is the length of the string, much like pressing a key on a saxophone changes the length of the column of air. The result is a more consistent tone and when done right, more legato phrasing.