I went for years without ever touching the tone control on my passive Jazzes, but just recently I've been exploring different sounds from the bass - Tone rolled all the way off, and just the neck pickup for reggae/dub numbers, and then tone at about 60% and just the neck pickup for a P bass sound-a-like.
I changed the value of the capacitor when I rewired it a while ago and forgot what I replaced it with - the cut-off frequency is a little bit higher than the 'stock' sound though, so even when it's at minimum I still get a little bit of extra definition.