Specifically, the new download later option applies to the following:
● Season Passes and completed TV seasons
● Complete my TV season or complete my Season Pass
● Movie bundles
● Music box sets, individual movies, and TV episodes
When purchasing any of the above items using iTunes 11 on a Mac or Windows PC, or an iOS device running iOS 6 or later, you’re now presented with Later and Download (or Download All) buttons. Tap Later and the purchased items will be added to your iTunes account and accessible to stream or download in the future via Apple’s iTunes in the Cloud feature. It’s a handy feature if you, say, want to buy a movie on sale while you have a spotty data connection; you can make sure to get the cheaper price, then download the item when you get home—or even just play it from the cloud.
More details can be found at the support document posted by Apple on Friday.