Only drinks and food there
And attractive female company paid to entertain you and put up with your drunken rants.
Sure, sure, most snack bars are clean, but the mizu-shobai spectrum goes a bit like this:
Regular bar with pretty waitresses < Snack bar < Hostess Club < Grope bars, Brothels, Soaplands and the like.
Both snack bars and hostess clubs are in a gray area, where they dangle the possibility that, if you're a frequent enough patron spending enough money on a girl, you might be able to take her on
offsite dates. Whether that actually materializes depends on the particular shop and the particular girl, with that being far less common in snack bars.
As a disclaimer, take what I say with a grain of salt, since most of what I know is from documentaries and articles on the subject. I've never been to a hostess club, and I've only been to a snack a couple of times, once by mistake, and once because it was the only thing close to a western style bar in a small town; and of course, being a lone gaijin (that is, not introduced by a japanese regular), I was treated as an amusing oddity, not as a serious customer to keep for the long term.