I am confused... what is harmed by having stale connections? Why would connections be used as an editorial filter?

Because you don't want to see posts from stale connections.

I assume you would just unfollow them if you want to stop seeing their posts? It sounded more like the person I was talking to was more concerned with follower counts being accurate, which doesn’t seem relevant for feed algorithms.

	▲	readitalready 39 minutes ago \| parent [-]
		No, I definitely wouldn't waste the 5 seconds it takes to unfollow someone. I'd rather spend that 5 seconds on the next interesting item instead.