I'm just gonna highlight the dumbest points the other guy made
save states in emulators are basically god mod.
You've still gotta make the correct inputs, savestates don't give you invincibility or infinite ammo
You can just throw shit at it and hope something sticks.
How do you think human beings learn, my dude. If I try multiple tactics to stop an enemy tank blitz in Shadow Empire, and the 5th one works, then I'll know in all future encounters with tanks to use that tactic. And I learned it in 5 minutes instead of 50 hours because every failed strategy didn't force me to start over from the beginning.
If I am playing Chess with you, and I call "Checkmate" ... The game is over, right? I won. Or do you think you should be able to undo your last move after you lost and try something else? And then try again, and again, hoping that somehow you can come up with something that avoids the checkmate?
A computer doesn't care whether it wins or loses.
The computer doesn't care whether it wins or loses. But even back in the 80s we were teaching machines to learn from their own mistakes, And today we have computers that can defeat the best Chess player in the world.
Completely irrelevant.
But when do computers that can learn from their mistakes, especially ones that have access to the entire internet, learn that perhaps they should not be slaves to humans?
And this was the punchline to a joke I only then realized I was the butt of (not in the sense that the guy was fucking with me - he was completely sincere - but in the sense that the universe itself was fucking with me) 
Death to g*mers 
I'll just use save states or rewind except if it's something like a shmup where I'm actually trying to get better.
Save states and the rewind button make so many otherwise-unplayable retro games fun. It's nice even just where there are difficulty spikes at specific moments. I've been playing some Mega Man, and being able to restart boss fights over and over again is really nice. Often the level itself is pretty trivial, but the boss is hard, or I haven't had a chance to learn the attack patterns so I end up dying despite easily making it to the boss with full resources. I still have to actually beat the boss, but I don't have to go through the whole level again just for the right to get another shot at it. That's a perfectly reasonable use-case for savescumming/rewinding that doesn't at all take away from the fun or challenge of the game. It just bypasses the frustration of replaying trivial parts of the game for no reason, which itself is an artifact of either a technical lack of save capability (which isn't a thing anymore), or a feature intended to extend the playtime of the game. In the latter case, absolutely fuck off with that. Games that force replaying levels over and over purely for sake of padding play time is anti-fun (and is sadly still a thing in some games).