Excellent to weed out unfollowers
When youre first starting out and following a lot of people in your field, craft, or whatever, you can follow many and weeks later, go through using Unfollow to weed out the unfollowers (theyre just succubae draining you out of the possibility of meeting someone whom you could later work with and you can only follow 5K people, and I know that sounds like a lot... but it isnt,) because of the aforesaid reasons.
Harvardchickie about
unfollow for Twitter, v5.5