I agree that the PA "should" do the bulk of the bass sound and that you only need reasonable stage volume..BUT, I am finding that many of todays clubs don't have the nice PA systems I was use to from back in the 80's when I mostly played out... This becomes a problem when they can't provide good bass sound to the club, since bass reproduction requires GIRTH to handle a large room.. So, I take it upon myself to take care of the bass sound in the absence of full sized PA's nowadays... If you can mic a SVT cab, that is the way to go..but to me a SM-57 doesn't cut it.. I would only mic if they have a EV RE-20 mic....
If I do go direct... I do so from the speaker output of the SVT head and then convert that to balanced low-Z XLR for the board..that sounds pretty good.. If the sound man is being a major shmuck with my bass..I just go out to the truck on intermission and break out the V4B cab..with it's 2x15" reflex folded horn enlosure, it's sure to rumble the bar bottles and glassware onto the floor
Chris