There are many operations where taking the tool to the material works better than the other way around. Long, wide or heavy materials mostly benefit from this. As mentioned, the quality of your result will be directly proportional to the quality of your reference surface. The tool will follow the material or the guide/rail that is fastened thereto. This is a big benefit for things like dados with a router as the small router base follows the irregularity of things like plywood and yields a more consistent depth. In the case of jointing, you are trying to create a reference edge or at least a true one.
"A hen is only an egg's way of making another egg".
– Samuel Butler