For me, when working on a song, it should always be about "Does this make the song sound better?" if the answer is no, try again, if you arent sure ask your band mates or the songwriter. The bass, like any instrument is about enhancing a song sometimes thats supporting, sometimes its carrying the melody. This is generally genre specific, so you are unlikely to have a 3 minute bebop bass solo in a thrash metal tune, likewise, in a folk band you are unlikely to have distorted two handed tapping basslines.
Jonny