I don't know about today's engines, but some early fuel injected engines would actually use more fuel when engine braking. In those early designs spark could not be cut off, so if this extra fuel were not added then the mixture would run very hot and risk pre-ignition and damage. I don't know about carbureted vehicles.

It only applies to mechanical injection and carburettor engines. With electronic injection, which is the norm since the 80s, this is not a problem.