I've heard the phrase "that black curtain really sucked up the light". I've got a shoot where the subject will be shot on stage with vast space around her and only shot waist up so I figured with the Coollight LED600 spot with softbox, I figured I'd just shoot with the grid attached but then wondered if it would in anyway decrease light output. Light should be just the same - correct?

There will probably always be some amount of light loss when using an eggcrate. I doubt its that much to worry about though.