I've seen the tippers at weddings I've gone to. What does it get them? Well, if the waiter is assigned 2 tables at 12 people each(Which is usually the case), it usually ensures that tipper gets served first. That water/drinks are replenished without having to ask for it. Simply put, more attentive service. For bartenders, it helps ensure you get prompt service when you go up to the bar.
I'm not saying it's rude or not, I'm just explaining what I've seen it gets you. Most of the weddings I go to are huge affairs in the NYC area, 150+ guests. When the table doesn't give that extra incentive, I can attest that it's harder to find the waiters, whereas when I've seen a tipper at my table, the service is much better.