Well, it is a feature supported by the box, and I'm entitled to my opinion and disappointment. I will give several use cases for why this feature is needed, IMO.
Use case one is straight out of Microsoft's marketing, but their reason for it fixes a real problem for a system with a heavy focus on online multiplayer. This feature will allow you to, as long as the game supports the feature and is working correctly, no matter where you are in the game, could be in the middle of a cut-scene or between auto-saves or save points, jump out of the game you are playing into and right into any random multiplayer game, then jump right back into the game you were playing before. It will pick up where you left off...or 1 to 2 seconds afterward. Not that important to everyone, but when I was into multiplayer, it could be irritating to either lose progress or having to turn down a request to join a friend in multiplayer.
Use case two, which I did not even think about when I made the tread, but with a service like Gamespass, you can play multiple games on the service without worrying about losing your progress in any of them, between 7 to 10 of them, no matter how different they are, as long as there is no update that game. It might not be as useful if you only play one game to completion before playing another one.
Use case three, since you can't count on auto-saves or save points to all be equal. Different developers do different things. Some games are good and will allow you to save almost anywhere at any moment. Some developers allow you to save your game anytime in a dungeon, and some of them won't. When a game supports this feature, while it is not as good as a save point or auto-save, you can expect that if you leave that game for whatever reason, you can go back into it later and pick up exactly where you left off. It can be months later, as long as the game hasn't received an update, you could have played something else in-between game sessions. Power outages or a need to unplug the console for some reason, does not matter. The game will be exactly where it was when you left. Multiple games will be where you left them. It makes every game that supports the feature pick up whenever put down whenever IMO.
The last case is part of the reason why I purchased my console so early into the generation. Though it did not work out entirely the way I wanted (None of the 360 JRPGs I have supports the feature, I don't know about Nier.), it has changed how I play games. Think of it like suspend on steroids'. You might disagree with it, but those are my use cases.