Quote Originally Posted by Eab1990 View Post
There is no in-game warning, but it's common sense that you gimp a character of 20 levels of stats if you evolve them early. I don't know why this is so baffling to newbies. If you've never played Fire Emblem, fine, but still, it doesn't take much to realize that those 20 extra levels aren't just for show.
There's more than one logic one could follow; like thinking that you continue leveling from 30 (or wherever you were) after CE. In that case it would usually make more sense to evolve units as soon as you're able.

There not being an in-game warning is either part of the design or a design flaw - but bad design in either case.