I never used to be a fan of auto-saving.
The last time I really experienced it was with Word, probably back on OS 9. The documentation for Word said that auto-saving would make your file bigger, since Word would not save the whole file, but only a log of your most recent changes. And there was a noticeable pause each time the auto-save occurred that was really annoying.
No thanks, I thought.
But when a perpetrator in my household who shall remain nameless jiggled the power strip enough to turn it off when I was writing a blog post in MarsEdit, after the cursing was over, I did think to myself, “It would be nice if MarsEdit had auto-saved that.”
I hadn’t read the MarsEdit documentation, and I hadn’t experienced any pauses while I worked, so I had no inkling that MarsEdit was in fact auto-saving my drafts.
When I reopened MarsEdit, it notified me that it had detected an auto-saved file, and showed me that file.
Rock on!
A brief survey of the MarsEdit documentation doesn’t reveal anything about this feature. I should know this, but can Cocoa do this automatically now? Is it so mundane that it doesn’t warrant mention?
More interestingly, does the auto-save only kick in when there’s a lull in user activity? That would be cool. Otherwise, I guess I can chalk up the paucity of pauses to faster processors and hard drives.
Weaponized Fluff 
Just popping in to say hi! I was the cheesecake-eating Asian dude across from you at the meetup last night.
Since the rolling blackouts, I’m paranoid about losing power, so I instinctively hit Ctrl/Cmd-S to save after almost every single damn change. So Autosave would be wasted on me.
I’m awful at doing backups, though.
The autosave feature does try to be smart about user input so it doesn’t slow you down.
Ideally you never notice that it’s happening — the only time you notice the feature is when it saves your bacon.
This isn’t a standard part of Cocoa these days, no. (But it’s not difficult to do, either.)