My (fretless) Jazz bass, instead of the typical V/V/T, is set up with master volume/pan control (-pickup selection/blend)/master tone. Up until recently, this was the only bass I had with more than one pickup in it, and the more-than-one-volume-knob thing would've tripped me up; I didn't wanna fiddle with/disturb output level while selecting pickup(s). -Like KG says, it's nice to only have one place to go for volume control while you're playing.
I recently modded the heck outa one of my W P-basses (the only fretted one) by adding a "mudbucker" in the neck (sorta like the one in Sheehan's "Wife" bass), and a MM in the bridge, making the original P split-coil the new middle pickup. for pickup selection, I added a Jag-style 3-switch plate to the north-east of the volume knob. Each slider switch turns its respective pickup on/off, but with a twist: when all three sliders in the off position, it defaults to the split coil P-bass pickup on without the tone control in the circuit.