I added a cover recently to keep my snowflake in, eels are notorius for jumping out, and I went from 3/4g per day evap to less than 1/4.
But... The lighting is not as good, it requires cleaning,gets salt creep, and is sometimes a hassle if you need to get in the tank (I do to feed eel) and is just generally a pain.
Tank temp jump about a degree or two also.