Previously, tvOS apps were limited in size to 200MB, but were allowed to download additional resources after being installed. This led to short initial installation times, but caused customers to have to wait for content to download after installing an app.
Apple is also allows tvOS apps to use On-Demand Resources to host up to 20GB of additional content on the App Store. Apple recommends app developers use On-Demand Resources to enable faster downloads. On-Demand Resources allow apps to do things like download the first couple of levels of a game and update as a user progresses, deleting content that's no longer needed.