Hypothetical Management Decision re: non-tipping patron of restaurant

[Golden_Rhino]

I have never worked in a restaurant, so bear with me. If a group of 6 guys tips 15% on a $500 tab, that adds up to $75. Assuming that the waiter only has one table (which is unlikely), and those guys hog it all night, is $75 that bad? I mean it would be for ~5 hours, which works out to $15/hour. Not a get rich sum of money, but not horrible either.