Downsides of "app maps"

I've noticed that some node frameworks (especially the ones implemented in TypeScript) always require you to register your components (controllers, services, ...). In case it's not clear what I mean, an example would be http://ift.tt/2wbGTeE Symfony framework on the other hand creates a "map" of all routes, hence it's no longer required to register your controllers. In case you're wondering: