How important are snails?

[asylumdown]

I've got like 6 of those big sand sifting snails. I can't remember their names, but they have smooth shells with leopard spots on them (bigger than all the other sand sifting snails). I also now have a copper band butterfly, which is a good eater, but not that quick so rather than polluting my tank by feeding too much so it gets enough, I've been trying to supplement it's diet with clams on the half shell, which it appears to love. However, within seconds of the shell hitting the sand, those big snails pop up out of the sand, and they basically smother the clam in a couple of minutes. This blocks any other fish from getting at the meat, and they don't leave until there's not a shred of clam meat left.

I'm tempted to catch them all and put them in the sump, but I don't know if that's a good idea, how important are they really?