Manual saving is a nice feature that I wish was in more games.

The auto save system in Bioshock Infinite drove me insane.

Or Game Genies!

Thankfully most of the games I play use manual saves. I cannot stand auto-saves... idk why but Ive never trusted them XD plus they always save either way before or way after I reach a certain area

Also games with manual save tell you you'll lose all progress after the last save, even if you saved right before it. Frigging confusing, and a few times my game actually did not save while I thought I had and thus lost a lot of progress. Save and exit option, only way to go to be sure.

I'm paronoid about saving anyway. We lost months of fun and hard work when our ps4 Minecraft got corrupted. Now I make a copy of it every time I exit. (Helps too with destructive kids) The nasty thing about one slot autosaves is that a power outage can wipe your whole game progress. Might need a warning on the box, do not play during thunderstorms.

Then you also have games that let you save manually, yet still reset you to the last checkpoint on reload, joy.

Autosaves + account system makes it easier for casuals, while RPGs and Visual Novels kept their saveslot tradition.

I guess it doesn't matter in a lot of game genres, missable trophies/success aside.

The bolded is exactly why some games need autosaves. I was playing Fire Emblem GBA not too long ago, and man does that game penalize the crap out of you for every mistake! It autosaves after every single action, so you can't just sit there and scum save files every time you do something dumb. My gf played it on the Wii U VC with save states, so she didn't get the same sense of urgency and how careful you need to plan every single move, because she just made a new save state at the start of every single turn.

Anybody who grew up with siblings and had to share games with them would have killed for multiple save slots in Pokemon. I'll never understand why people think having only one save slot for a single playthrough at a time is ever a good thing.

Several times I've tried to save in recent years and not a feature so go "Crap...when was last auto-save?" and end up playing not because I want to, but because need to get to next one to be able to turn off system without losing data.  If I am really tired I have put PS4 in sleep mode so can hop right back in next day, get to auto save and then feel safe won't lose data. Just cross fingers no major storm and power outage during that time.

I prefer manually saving over autosaving and multiple save slots are always nice

There are many games that do both manual & autosaves, they have the best of both worlds.... but yes it does seem to be rarer.
If it lets me I usually save 2-4 copies of the same playthrough, either by double saving when I quit or by rotating the overwrites.