Basically swap gives you options. Instead of the OS saying, no you cannot launch anymore apps, you don't have the RAM for it. Or just giving up and shutting down (like windows does, wink) when it runs out of resources. Swap gives you a sort of fake ram. And space for other things where none may otherwise be available. encrypted filesystems? compressed read-only media? You don't always need it, and if you do need it regularly, you might consider other system upgrades to manage that. But if you need it and don't have it, that's a bad thing. Windows has swap too, but when you're trying to be RAM, using a file on a filesystem that's slow as molasses creates a bottle neck that amplifies the need for swap. Sometimes beyond being useful in the first place.