For all the people wondering about how space issues will work with required installs, it's possible that if it runs out of space, it'll remove the least recent game and installs the new one.
So if two years after launch, you get home with your new copy of Halo 9, but only have 3GB of HDD space left, it'll be like, "You haven't played this launch Durango game in 18 months" and delete that.
And if you ever want to play it again, it's not that big a deal, since it installs in the background, and the game starts a few seconds after putting the disc in.