In the past, Android apps have been limited to a 50MB file size. App developers who needed to add extra data, as is the case with most big games, would have to have a secondary, self-hosted download after the user first launched the game. Today, that changes with Google introducing support for up to 4GB of "expansion files". While APKs must still be under 50MB, Google will host two 2GB files that include extra data for developers' apps. Nice!
This will solve a lot of problems for a lot of people, not the least of whom are developers. Since Google is doing the hosting, it's no longer necessary for a game developer to host hundreds of megabytes, or even gigabytes of data on their own servers.