I like tipping at bars and restaurants: it eliminates the middle-man between me and the person providing the service, and I can reward (or consequently punish)

I like tipping at bars and restaurants: it eliminates the middle-man between me and the person providing the service, and I can reward (or consequently punish) servers who provide good or great (or poor) service. But in other cases, I see the tip line and click Zero. It makes the math easy.