People on here can be absolute shites about who follows you (despite this being out of your control) and will add you to shitty block/harassment lists based on it.

unfollow provides you the agency to determine your timeline interaction horizon (who sees your posts in their timeline) without recourse to the blunt instrument of blocking (commiting serious offenders to the void, who can never see your posts again and you not theirs)

They are no longer counted as a follower in the latter instance. As things Ard now, the Follower count is massively inflated with account that are blocked. If removed, it would go way down and show other people accurately how many follow me.

they won't be able to interact with you at all anymore