@MomtoAndrew2018 It depends on the school. Case Western, for example, is very sensitive to “demonstrated interest,” because it is aware that high stats kids treat it as a safety school, should they not get into a higher ranked choice. The ultimate demonstrated interest, of course, is to apply ED but that locks you in and IMO, it would not be in a university’s interest to award merit scholarships to ED students, because they don’t have to be lured with merit. In theory, they’re a sure thing.
Case’s application involves no supplementary essay and I believe there’s no application fee either. So (again, just my opinion), putting in an early application might suggest seriousness about the school. Applying right before the RD deadline suggests that it might be an afterthought.
Anecdote - my daughter applied EA and got a substantial merit scholarship. Two other students I know who are of similar caliber who applied RD were waitlisted. Yes, I know that anecdotes are not data. 
As to your broader question, there are some places where EA is more competitive than RD (Notre Dame, for example).
What’s in it for the school to have an EA round? It’s a chance to lock in part of their class early on. I think there’s a psychological benefit for students to get an early acceptance - it gives them more time to imagine the school as a place they might attend. There is more time to plan an on-campus visit that might seal the deal.
As for Case, I think it might be a bit of a reach for your son, but worth a try. The application is easy through the common app. It is a wonderful school, IMO. It ended up being my daughter’s second choice. The Maker space is a fantastic resources and there is an energetic feel about the student body. While known mostly for tech, liberal arts are strong also. There are no barriers to entry for specific majors. It’s in a relatively safe area of Cleveland with a large park and lots of free museums nearby.