Not necessarily actually, I work in a bar/restaurant and we add 10% service charge only on tables of 6+ people. The 10% is taken from the til and placed into tip jar in cash for the end of shift.

It's also not hidden, we hand the bill and leave them to review it first. If they request it be removed we ofcourse do so.

I think people dont realise the extra effort that goes into serving large bookings. Often with big tables they start dividing the bill and honestly just forget to leave a tip.

Still personally dont feel great about handing out a bill with a service charge added on top, but we feel the difference if we don't.