The fixing bolts on both disc calipers fitted to my bike came with circular spring clips fitted over the top of them, which I’d barely noticed until I saw one was broken while I was cleaning the brakes.
They appear to serve no function that I can see, other than maybe to dissuade you from fiddling with the bolts.
Any reason why I shouldn’t bin ’em?

Stops the retaining pin from falling out. I never bother.

I’m on about the bolts fixing the caliper to the frame, not holding the pads.
Perhaps “spring clip” is the wrong term, but I don’t know what else to call these things! Never had them on any other bikes.

the plastic clips.

supposed to be anti rotation – reality do nothing if your bolts are done up right.

Black plastic bits? Supposed to stop the bolts coming undone just use loctite and chuck them they never stay put for long.

oh those? never bothered with them either.

older ones had holes in so you could wire them together.

Sounds about right. Cheers! 🙂