I don't understand your question, I think.
Disney offers the Opportunity to make Advance Dining Reservatioons (ADRs) 180 days in advance for folks who wish to make them. For the popular in park and resort restaurants they frequently fill to capacity by people who want to assure they can eat in that restaurant, on that day, at that time.
I don't know of anywhere (except maybe V & A's ??) that requires reservations. It is just that they fill with people who make them, so it because necessary.
Is that what you are asking?