Slugs as well as snails can climb, so they can come in the top of the window if it's left open. We get huge snails inside our bedroom, and if we don't notice they end up as empty shells stuck in obscure corners, having dried out with nothing to eat.
Leopard slugs are also known as Great Greys, or I assume that is the ones you mean. My OH loves them (not as hors d'oevres though), and they do seem to munch their way through lots of those horrible tiny fawn slugs which demolish lettuces, so I let them be too. However, they like a bit of salad themselves after the main course so they get turfed off my plants.
We have loads of the big black slugs in the veggie patch. In fact we have more slugs of every sort than we have ever had before and I'm despairing for my few crops. Maybe we should get some ducks again