I believe that every action everyone of us is taking has some long term effect in ourselves and in our society. So, we should not simply neglect things (no matter how small) in our daily lives. Just repeating some actions blindly would easily lead to large harmful effect. For example, when you are exercising if you do not know why you do it, or what effect it should have (e.g., which muscles should move,) you could simply hurt yourself, while you expect the exact opposite.
In taking every action, I have a simple rule; either I should understand the reason behind that action and/or understand the impact it should have on myself and/or others. I don’t think we should obey rules simply because they are there. These rules sometimes are written and sometimes are just “common sense” of our society. Traffic rules is an example of former and paying tip at restaurants is one example of latter.
I don’t think we should pay tip because everybody does, nor we should pay tip because the person doing his/her job. Paying tip should be in response of person creativity in his/her serving. Sometimes the person who is serving you bring you something beyond what is your asked for, it just complement your food by some drink, or desert, or something, then this person deserve to be thanked for doing beyond his/her responsibility. Perhaps, the ideal case is the waiters make something homemade to bring with serving food (it could be as simple as tea).
Note that giving tip is not just for showing off OUR generosity, but, it is a sign of appreciating someone else jobs. Giving tip is a good action, however, it can simply lead to terrible results just for not knowing why we do it.
On the same note, we should also understand why we pay tax, why we go to school, why we eat or don’t eat something, and finally why we live.