Auto aim to remove any chance of me blaming the game for its failures, because it'll be all on me when I fail a mission. It certainly didn't help in Red Dead Redemption, that game is just ass to me.
If I choose to play with a mouse and keyboard on the PC version, I'd probably play with free aim. Given the platform, head shots just come naturally. If it could auto switch between two control schemes, then great, but I doubt that'll happen.
Well, if I'm already not enjoying playing a game (Red Dead Redemption, for example) and already know what happens near the end, then no it don't matter, son.
If I do get spoiled over something I intend to visit or invest time into, then so be it. If the game, book, film, or whatever isn't doing enough to keep my attention throughout the journey, it probably wasn't worth getting into anyway.
If Breaking Bad or Game of Thrones have the shittiest endings, which for some reason I'm expecting so my hopes aren't dashed so easily, I'm not gonna lie and say it wasn't worth getting up to the ending with all the crazy theories and parallels from beginning to end.