Dry ice is just carbon dioxide compressed from gas to a solid. So when it evaporates it just transfers directly to a gas, leaving no residue. It is usually a lot cleaner and has a higher yield than bubble hash.
I would suggest looking up dry ice hash, it's a lot less labor intensive and imo tastes better. Basically the hardest thing about it is finding the dry ice if you're in a rural area.
Haha, yeah I guess dry ice has a bit more of a safety factor than just plain cold water. But it really isn't all that dangerous with some basic precautions.