1. That I actually fully own the copy I buy and can do what I want with it. That means no "constant internet connection", which means that the game might be unplayable at a future date or even days with bad connection, and no "can't resell" BS.
2. That I don't have to install additional software, either third party online crap or local pests like StarForce. GTA IV is a perfect nightmare example. "No, I don't want to install Games for Windows, I just want to play the game". "No, I don't want to install Rockstar Social Club, I don't care about "sharing my achievements", I just want to PLAY THE GAME". I couldn't even start the game without installing a patch through GFW, which it initially refused to do since I apparently didn't have something called "Silverlight" installed. That's four additional installs before even getting the game to START!
It's one thing if you're asked to install GameSpy Arcade or whatever, which you can just decline and never hear from again, but when you're actually forced to install additional programs just to get the damn thing to work, that's more likely to make me hate the game before even starting to play. I will never, ever give Rockstar my money again for this simple reason that GTA IV pissed me off so much with all the surrounding hassle. And now UbiSoft can also go to hell after killing Silent Hunter V.
So what happens if you lose the disc or it gets damaged at least then you dont have to worry about playing the game. I doubt anyone would be happy if they had to fork out ANOTHER 40 quid or whatever because these things sometimes happen. That's right, once the game is installed you don't need the disc.