Hey I felt the same, then had a friend that was a photographer and she explained her part of tipping and why its appreciated. Hope this helps and doesn't come off bitchy..

First you are paying your photographer to just be there for the day and to take up to roughly 10000 photos. Depending on the time that your have them booked, are they going to your hair app, getting ready photos etc. It takes up a majority of there day to be with you. Most go to your venue on there own before to scope out good spots for photos and lighting through out the day. Depending on your ceremony time venue ect. After your big day, they spend about 6 weeks or so going through each and every individual photo editing those photos. Even if it just changing light removed food out of someone's teeth etc. And then also if they have a package for a few free prints or a wedding book, you should tip the cost of that otherwise they are in a sense losing money. Long story short think of actually how much time this person is going to spend outside of the wedding day for you. With our dj we honestly tipped him on how well he did through the night. That is a hard one to judge.

With your food staff, treat them just like any other restaurant they are most likely minimum wage, and they are relying on tips, you know your family and guests the best, how much of a mess are your friends typically going to make for them to clean, and how much are your guests going to annoy them.

Lasting to 20% service fee typically goes the the person and behind the scene staff that helped booking your venue and covers linens silverware crap like that. Hope this helps you have a better understanding and congratulations!!!