Although tipping is technically optional, it is expected unless the services was particularly poor. In fact, tipping is so standard that there are laws that take this into account – whether it is the law that allows a lower minimum wage for waiters since there is a presumption that they will receive an additional amount as tips, or the fact that waiters have to include a certain percentage of the bill for tables they serve in their taxable income, since it is presumed that a tip for at least that amount was received – and as tips are often paid in cash, it would otherwise be easy for the waiter to just not report and pay tax on such income.
So yes, tipping wait staff properly is not only an issue of being a “mentch” – if you don’t do so, you’re litterally taking money away from such staff.
an Israeli Yid