[richev]

I've always understood that this person's actual job was making sure that no-one was taking drugs in / vandalizing / doing anything illegal in the bathrooms.

They're there so the owner of the club/restaurant can relax, not you.

[rkuykendall-com]

If this were true, there wouldn't be so much emphases on tipping.

Right now, I feel like this guy is useless and I don't want to give him money and I feel bad about that, like by not paying him I'm calling him useless.

If it were for the owner, and that was clear, I'd feel great because I was making his job easier by not causing any trouble or mess, and on top of that, hey thanks for the towel!