While I don't have any they do protect the spokes, the mech and a good ride.
You're nick name for it is new to me though, they've always just been called spoke protectors.
I've seen an old man down the street where the chain came over the top (mech setup was fine, it just bounced off) destroyed the wheel, snapped the rear mech and destroyed the chain.
Made me late for work trying to help him.
Also seen the chain come off over the top on plenty of our ride, happened to me. Even well setup mechs are not immune, if it's bouncy terrain or grassy, twiggy, it can bounce off or get derailed.
This is what can happen
(no vouching for that mech being setup correctly, but as far as I know it was.)
of course, I'd still not have one, it's just not retro.
I leave it on my old mans though, function over form is better there.