A recent steamOS update said it was laying the foundation for hibernation, which should be a more battery friendly alternative to sleep.

The second part depends on the game, some will just work. Others need to run a first launch script and install some stuff before launch, which I agree should be part of the download process. Finally some games require license check or additional network access on first launch while the game is running, and this part can’t be automated by valve. Overall it’s just a good habit to always run newly installed games once, at least long enough to get to the main menu.