This is not just for games you've "already played." I'm primarily a PC gamer now and features like this are one of the biggest reasons I switched back when this stuff wasn't so prevalent on consoles.
Here. Let me paint you a picture for those that are having a hard time understanding why this is so cool for lots of people who aren't swimming in cash.
let's set up a 5 year timeline for a random person. I know MANY people like this.
Year 1. Person makes 50k. No outrageous bills. Is able to buy every newly released game that interests him.
Year 2. Person makes 50k. Health issues pop up. Bills increase a bit. Is still able to buy every newly released game that interests him but not as comfortably.
Year 3. Company downsizes, person loses job, has to relocate, now makes 40k. Bills are same but money is tighter. Can't afford nearly as many games. Way less time to play them due to new job. Just buys those that GREATLY interest him.
Year 4. Person makes 40k. Health issues rear head due to new work environment. Car accident. Bills increase quite a lot. Can only afford a game every couple months. Hunts for deals and sales as much as possible.
Year 5. Person makes 40k. Married. Saving for new house and kids. Bills are back to normal. Due to saving, can't afford many games. Services like Gamepass and Humble bundle are a staple now. Discovering all kinds of games he never knew he'd like though.
People like me don't have the money to buy every flipping game as it comes out nor do we have all the time in the world to play them right then. Our budgets and expendable time increase and decrease all the time. So we have to pick and choose. I've personally missed out on a lot of series that interest me. I haven't played MANY of the Final Fantasy games for example, even though I've been interested. And due to gamepass and such I can now try out tons of games that I otherwise wouldn't have known I'd like.
Oh, what's that? X Publisher is having a sale? They are bundling a bunch of games in a series I haven't played before the launch of the newest, shiniest, cool looking one that comes out on next gen consoles in a couple years? Sweet. I can afford that now. I'll get it and add it to my backlog for when I have the time to go through them.
But wait, there's more! When I do have the time, and I've upgraded my console because I now have the funds to do so, I get to play them in better fidelity and with more features than I would have all those years ago if I had gotten and played them right at launch on the console they released on? Freaking amazing. Not so bad that I had to wait all this time now.