Tipping is mostly because of the low profit margins for restaurants and the resulting low wages of the servers. Servers in Michigan make far less than minimum wage and make that up through a 15% tip.

Now not all restaurants are equal. When I go to Leos Coney Island Im likely to just give the server a 20. If I were to go to a chain restaurant like Red Lobster, those servers make much more than a Leos server and Id leave the 15% to 20% depending on service. But If I go to a high end restaurant at a resort or in the city those servers get 10% max. If Im spending 250$ or more on drinks and a meal for 2 that Restaurant can pay their people more.

Anyway thats how Ive always looked at it. And I always tip in cash never on the card. Let those people hide some income from the beast if they want.