Since your games will work on any X1 with just your login and without the disc, there has to be a check-in system even for single player.
Basically any kind of cloud access, be it to games, saves, or what have you require online.
I actually find the policies convenient. Swapping game discs when switching games on PS4 is going to feel as archaic as listening to music on a CD. Instant switching between games is the future, and having instant access to your games and media regardless of which X1 machine you are on is also the future.