DEUT304 Nachmanides comments, “The meaning of this verse is as follows: First, God tells you to keep the statutes and laws which He has commanded you to. And then He tells you that even with regard to those matters concerning which there is no specific command, you should see to it that you do only that which is good and right in His eyes, for He loves that which is good and right.” Thus, there is no law mandating that we leave a waiter a tip. But waiters' low salaries are based on the presumption that people will offer gratuities. Therefore we must do the "right and the good" and act generously.