To those unfamiliar with them, toaster ovens sound like a combination in and of themselves, but this isn’t precisely true. A toaster oven is, at it’s most basic, just a small oven in which bread can be toasted. By contrast a combination toaster and oven is a toaster oven with a built in slot toaster that is otherwise identical to a stand-alone toaster. Combination toaster and toaster oven models are great for quickly cooking a small breakfast with toast on the side.
A microwave toaster oven combination switches from one kind of heating process to another; that is the direct radiation heat of a microwave and the oblique, heated air circulation of a convection oven. The two don’t work in tandem, so the only advantage is that two separate units don’t have to fight for space in the same kitchen.
Other kinds of oven “combinations”, such as oven/broilers or rotisserie ovens are actually just functions of the oven rather than a genuine secondary mechanical function.