While root notes are (generally) easy, it tends to get REALLY boring, especially if it's a slow song like...say...Truly Madly Deeply or something original. If it's something original I tend to start out with root notes to get a good feel of the song, and then when I'm familiar with the chord changes I start throwing in extra notes here and there until I have a bass line that is pleasing to the ear.
Of course, when it's a cover of a song like Truly Madly Deeply, it is BORING as hell on stage to be playing one note ever 10 seconds or so, and it's just so much fun to modify bass lines.
Heck, I did it with Truly Madly Deeply for the original singer of our bad who was/is obsessed with that song. Too bad he booted me for one of the 12th graders that plays bass. Oh well. She wrote a pretty cool sounding bass line for it, too.
Yes, SHE.
