"Saving" on Obsidian - please explain for a noob

Hi guys,
it’s just been bugging me and can’t find the answer.
Love Obsidian and use it all the time.
But no other program I know lacks a ‘save’ function. I don’t know why that’s strange to me, it just is. I would like to know about the reasoning, the functioning aspects of it.
e.g., if it has an automatic save, is it instantaneous? And why don’t any other programs have automatic save?
Maybe there’s some foundation-level principle I’m oblivious to; I hope someone can enlighten me. Thanks!

Obsidian automatically saves and pretty much constantly. I’ve never lost a single line. But as far as I know you can, like in pretty much any other App, use Ctrl/Cmd+S to save manually.

OK, thanks. At least now I know when I hit ctrl-S, i’m not just twiddling in the wind, or whatever the saying is.
Why isn’t every program like this?

You can test how fast the auto-save is by writing in a note and closing the app right after.

On macOS, every app is. I can’t remember the last time I thought about saving a file manually. So perhaps just different OS experiences?