Sand or no sand

[molly]

I've discussed this before, but i'd like another opinion. I've removed the sand from one of my 20gl. nanos. It's doing fine. But it looks bare, and not complete. I'm thinking of adding sand back to the tank. I've purchased some live sand, and want to know the best way to add it back to the tank. Remove the rock and coral? Why is it that some fish stores beleive in sand bottoms, and some don't. Is it a perference, or is there a big difference? I'd love to hear your opinions, Molly