Yep. I do.
For one, I like different basses. Actually, I like basses, period.
Secondly, one can be used as my spare in case the other one can't be used for whatever reason.
One is active, one is passive.
One sounds modern, one sounds classic.
One is lighter, one is heavier.
One is cheaper, one more expensive.
The first one is an Ibanez GSR200FM, which I sometimes tune DGCF for some songs that require that lower D. The second one is a Fender MIM Std. Jazz, which I always leave on EADG.
Eventually, I'll want to add a 5-stringer and a fretless. Possibly a short-scale too.