There are two main reasons I would remove the glass top on any high light planted tank.
1. The glass blocks at least a portion of the light, or least reduces the intensity that drives it to the bottom of the tank. Especially if its dirty.
2. I hate cleaning the darn things. Its just another maintenance chore I choose to avoid.
1. I never seen a significant difference in evaporation rate or tank temp with or without a glass top. But, I have also never had a real tight fitting top that went all the way to the back.
2. I like the reflections on the ceiling from my MH tank.