Well, impaction isn't the only reason you wouldn't want to house on sand.
Sand is basically like forcing your dragon to live in a litter box. No matter how soon after your dragon poos you clean it up, there will always be a liquid that gets in the sand, and then germs spread, and it gets worse, and your dragon can get sick.
Tiles are much safer, and more sanitary. Plus there is no dust with tile, no chance of sand getting in the eye with tile, and tile even keeps your dragons nails in check.
Dragons actually live on hard packed clay in the wild, not sand.
I still say dump the sand when you get him, tile is only like 10 bucks to have enough to cover the entire tank. Much less than it costs to constantly be buying sand because if you are using sand, you should be totally replacing it very often, which gets expensive.
I understand how some people haven't had problems with it, but there are problems they might not be aware of. And the fact that some people have had problems with sand, is enough to make me not want to risk it with my dragons.
Oh, sorry for the long post lol.
-Brandon