So if a user source can emit normal events
How did you arrive at this conclusion? A user source can only emit user events.
Well, looking at the source I guess it would work. But that's an implementational detail, it certainly is not documented. Nvm, it is not guaranteed to work.
Either way, user events are useful because they have 4 separate data fields that you can fill with anything you desire. No other event type has the same.