Is a lid necessary?

Just curious - I've seen a lot of setups without lids and I've always wondered whether or not it's necessary.

I've got a planted tank (trying to grow a carpet right now) with a powerful LED light. The fish I have aren't really known for jumping (1 gourami, 2 gold barbs, a handful of mollies, an african knife, and a handful of cory catfish). Is having a lid really necessary? I'm sure I'd get better light if I got rid of it - that's why I ask.

Thanks!