I thought it about it on my small 5g fresh water tank, the I keep a lot of plants to help keep water clean. If you have a marine tanks with invertebrates don't they need sand, like narcarrius (sic) snails? And any algae growth on the sides will now be growing on the bare bottom, and try keeping that clean! I think there are some good points mentioned previously about the upside of a sand bottom (ph), and one consideration is appearance. Most tanks don't make an attractive bare bottom, but the sand gives a nice background/bottom appearance. To each his own!