There is one downside to downloading games. It sometimes takes a bit of time, and when you're juggling your gaming in between school/work and other responsibilities you want to get as much out of your gaming time as possible. Therefore it should come as good news that the latest beta version of Steam allows you to start downloads remotely using any web browser (for instance on your mobile), so that you can start gaming immediately when you get home.
You can find out more about the latest version of the Steam software over at the official forums.