Oh, well, lets see...
You could create a map where clicking on a blank bit of space creates an asteroid there. :>
You could create a map where clicking on a blank bit of space creates an ever-increasing gravity well at that location, peaking after 10 seconds before subsiding again. Imagine what that would do in a map like Big Bang :>
You could also create a map where clicking on the background causes the background colour to change. Why is this useful? I haven't the slightest idea. :> But I'm sure it will come in handy for something !
What else, hmm.. you could have a map where you control a single, uber-tough Laser Mine. When you click somewhere, the mine's "asteroid" (the one it is orbiting) moves - drifting toward the clicked location - although the player wouldn't see this as it has a radius of 0. All the player would see is the mine moving about. :> You could build an arcade-style see-how-many-seedlings-you-can-flatten level.
Imagination ftw !