You misunderstood.
12GB super slim doesn't have enough space for monthly IGC downloads right?
You don't have to download and play the games and delete every month fearing the game will disappear after that month . Just flag the game by downloading and cancelling the download. Th game still gets added to the download list it can be re-downloaded any time even when the game has been moved from IGC list. Pretty standard. I do that too since I don't have a lot of space left on my 500 GB disk. Around 20-30 GB left. So I flag everything and download later to play.
In a nutshell not mandatory to play and delete immediately on smaller sized systems.
Download List is tied to one account therefore can be used to redownload any time.
I know you are aware of that I wrote for the newer members.