I have a good friend who doesn’t believe in tipping waiters 10 percent. It’s not that she’s stingy - far from it. I’ve seen her leave $10 on a $15 lunch. It’s just that she believes that you should tell the business exactly what you thought of their service, not what they think that you should pay for that service.
According to her philosophy, the tips show the restaurant what people really think of their service. If the waiter was excellent, and the service was amazing, she gives generously, and not only does the restaurant know that they has done well, she’ll tell her friends about it. If the waiter was rude and the service was poor, she will give very little tip (and in one memorable instance, no tip at all), making sure that the business knows that they did extremely badly - and she won’t go back there again, or take her friends there.