Oh we provide our own PA, but I'd still never turn up at a pub/club gig without backline.
For larger pubs we have a big Markbass PA that is also a superb bass rig, but for larger pubs that puts me behind the PA and standing next to a loud drummer, so I still want my own backline.
For smaller pubs we take our vox-only PA so ... backline.
One thing that really works for me is consistency. If I take either the same rig, or at least the same structure, to every single gig, then I don't need to waste time & energy at each gig trying to remember what I'm doing and how it all plugs together. So at every gig I play I know that my basses must be plugged through a head (which varies according to what sort of gig it is) into a cab (which varies according to what sort of gig it is) but always using exactly the same cables and sequence.
Perhaps I should mention that at bigger gigs I also take a DI feed from the head and run that through the PA as a matter of course, but that's something that's a bolt-on to the backline, not the other way round.