In regard to venues that aren't designed for bands; you will encounter such things as;
Having to unplug the cigarette machine (do they still exist?), or fruit machine, in order to power the whole band from one socket.
Arriving in time to set up, only to find that several people are eating meals in the "stage" area.
Access to/from "stage" is via crowded dancefloor.
Access to toilets is via "stage".
Access to fire exit, which you mustn't block is, via "stage".
"Stage" is area in corner, behind pillar and cut off from main bar area.
However, apart from the aforementioned diners, you will enjoy the freedom of setting up as you like in your own space (the size of a matchbox), without being hassled by sound engineers and musicians from other bands.
Have fun!