Most (definitely not all, but most) TS breakfasts are some variety of all-you-can-eat/buffet.
They definitely do not include dessert, in the traditional cake-pie-creme brulee sense, but they do include fresh fruit, sweet rolls, pastries, and other "sort of like dessert" things.
As for being a waste of a TS credit, most of these are character buffets or other similarly-higher-priced things, and so no - I would not necessarily call them a waste. Breakfasts are lower in cash price than lunches and dinners, of course, but still in the $20+ range for adults.
CRT being a double-credit meal, on the other hand, is wasteful in general, breakfast or otherwise, if you are looking to maximize the cash value of what you spend your credits on. The cash price at CRT, especially for breakfast, does not generally exceed the cash price of two separate dinners elsewhere.