That's only so the server can explain what you are and are not entitled to while on the dining plan. So if you ordered an appetizer, the server can remind you that's not covered under the plan. Or if you didn't order dessert, the server can remind you that is covered under the plan.
Having the dining plan doesn't make your service and better or worse and your food portions are the same size and anyone else's.
In the past, some dining plan participants were afraid that their service was not up to par because the gratuity was automatically included so why should the server work any harder because they already knew what their tip would be.
A very good example of this is dining at the Biergarten. Eight people, some on the plan. Our server worked just as hard for them as they did for us. Same with the Japanese habachi place. We were the only two NOT on the plan. Didn't see any difference at all.