[warvstar]

No downloads and the ability to easily and quickly jump into the action, especially useful for multiplayer or social games.

[sheepdestroyer]

You're maybe not saving the game to disk, but you still have to download it. At least the assets you're going to interact with. And if you want to play again, then you keep the game/assets in a browser cache somewhere and there's not much difference with downloading and installing the game, in terms of bandwidth/diskspace

[JoeyJoJoJr]

Of course, but from the user’s perspective this is all transparent. Parent comment is talking from the UX perspective.