Possibly Helpful, Definitely Annoying

Long ago, before everyone had a computer in their pocket, people used words to convey ideas. Often, these words were written on paper. Occasionally, these words on paper were spelled incorrectly. The only thing to do to make sure that the words you had written on paper were not spelled incorrectly was to ask someone else to make sure. If there were corrections to be made, the words needed to be rewritten on a new piece of paper, or crossed out and the correct word rewritten nearby, or white-out applied and the correct word rewritten on top of the incorrect one.
When I was in high school, this was how assignments were completed. On rare occasions, we were allowed to turn in assignments completed on a computer.
Misspelled words typed on a screen are more easily identified because of the red squiggly thing that underlines them. When you use words to convey an idea on a computer, you don't have to get someone else to make sure none of your words are spelled incorrectly, because the spell checker does that for you.
When an automated spell checker was first introduced, there were no squiggly lines. You had to remember to tell the program to run, just like you had to ask someone to look over your words written on a page. If you forgot, there was no way you would know how many times you'd spelled "definitely" wrong in your English paper. You'd have to wait until Mrs. Lamson handed it back and reminded you that it doesn't have an "a" in it and has only one "l."
I have no experience with the early days of autocorrect software; I stayed away from smart phones for as long as possible for that very reason (among others). Autocorrect doesn't let you forget, but if you skip the bit where you double check that text to your boss, you may be sending him something incomprehensible and weird. From what I understand, autocorrect is supposed to learn your habits and most frequently used words and extrapolate based on those patterns to guess what you mean when you misspell something. Only, I don't misspell things often, and when I do, I mean to. "No, autocorrect," I say, "I didn't mean 'pull lease,' I actually meant it when I typed, 'puh-lease!'" But it's not like autocorrect is listening to me even when I do try to instruct it during these moments of intentional misspelling. I can't say, "Just trust me, autocorrect," and have it leave me alone about how I like to hilariously misspell certain words. I suppose some people definitely have a use for it, but I just find it mildly annoying.
Some days I think I'd like to turn it off, but then I won't be able to tell future generations how much it bothered everyone when they're complaining about their thought-to-text software. "You think that drives you nuts?" I'll be able to say, smacking a dictionary down on the table in front of them. "Let me give you a few links to some 'autocorrect fail' websites!"