It’s clear to me what the Auto Keyframe button in the timeline does.
But what about the big ‘Auto Keyframing’ button in User Preferences -> Editing? To me, enabling it doesn’t seem to make a difference.
Is it related to the (strangely located) Auto Keyframing Mode (Timeline header -> Frame)? Though that seems to work fine without.
A bit confused here…
So I guess it’s a mystery not only for me!! 
that’s a mislabelled button, what it should actually read is: open dimensional portal for the hostile aliens to come and take over.
Really? Then I expect those aliens to be really pissed off by now. I’ve been pressing it on & off continuously. Imagine the portal closing every time you’re about to go into warp
Any other possible explanation?
The real purpose of this toggle is that it is used to specify whether auto keying is enabled for newly created scenes. Once a scene has been created though, the auto-keying toggle in the timeline is the one which actually controls whether auto keying will be used when doing stuff within that scene.
Ah… I’d always wondered that myself.
It is a bit confusing.
Ah, so that’s it.
Yeah, that’s not explained at all in the tooltip, and I wonder if it’s really practical (since it only works on new scenes, not on new files).
Thanks!