Due to injury I constantly switch between using 3 or 4 fingers. With a broken pinky (further compounded by dupytrens) i have no real strength or flexibility in the 4th finger so I look on enviously at you lot walking up and down the fretboard like spiders! I keep trying with 4 fingers but can only get consistency (clean notes) with the first 3.
I look at some players (latest was Sean Hurly on youtube) who seems to play effortlessly without even separating their fingers. Sure, they tend to be people laying down a simple solid groove rather than virtuoso noodling but hey I could live with that.
Whilst 4 is best i guess there are a few of us who get by with 3. Frustrated sometimes maybe but gotta play the bass.