That's a good point, if you write a script to unfollow friends after about a 100 friends you will get an error. And that is a daily maximum. You have to wait another day to remove more. So if you have 2,000 friends you will need to focus for an entire month to do so.

At the end of the day unfollowing simplifies your timeline which lowers your engagement. The same applies to unfriending but I didn't mention that.