there is so much tonal variety in the P-bass, i think it is forgotten sometimes
for me, here's how it is (with roundwounds*), starting from rolled all the way back:
0% - for jazz, some motown
20% - motown! all the way. little bit of grind for ya. still old school enough for some jazz tunes.
40% - Sabbath style rock. also good for old, Curtis Mayfield, Sly & Family Stone style funk.
60% - bit rocky, still a little funky. play up near the neck for Gezzer Butler heaven
80% - pretty open now. if a pick is your thing, you'll do well here. Think Dave Ellefson.
100% - Wheee! ROCK is the key with this setting. up near the neck you get nice clunky finger noise. Mmmm
*generally play flats these days. but i only use my P for 'older' type stuff, these days, too