That is nuts, is that common in the States or just in your region? I know Canada wide you will have P.A support unless the bar is a dive or in a population of less than 500, at least in my experience.
Saves the bar a lot of dough though, no P.A upkeep costs or soundman costs!
That is my experience too. The nicer places even have a house drum kit, house bass amp, maybe even house guitar amp, and of course a house grand piano. (not 'beer guzzling' joints, but more like restaurants with concert stage and drinks served)
Anyways, different places....
The other case, already referred to, are places that usually do not have live music, like art galleries, reception halls, hotel ballrooms rented out to a variety of people etc. They may have equipment that they can supply for a fee, but might was collect that fee and supply it ourselves.
But there are some funny comments about singers without mics and all. Ha ha. (BTW the whole band benefits from the bass rig, and the whole band benefits from the drum kit too. The basic essence of the PA is for the singer, it is the singer's combo-amp-speaker. That's it. Every singer performing in the amplified styles should have a mic, a cable and some way to EQ+amplify with the reverb that they want. As things get louder, then the whole group can scale-up and re-purpose equipment as needed. )
We all should be prepared to supply what is needed, but also be smart to seek out the opportunities where what is needed is already supplied. And the more scale-able our systems are, the better. (Just because we have equipment, does not mean we have to use it every time.)
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I think a venue that wants live music repeatedly, ensures a better overall experience for it's clients and hence makes more money long term by having an in house PA that is right for their place. The sound will be appropriate at all times, physical space can be optimized, set-up, take down, sound check is reduced, and per band payout could be a little less each time because the venue supplies the basics. (Musicians happy to play for less, because of less schlepp).