Looking at the occasional new post to an old question that I've followed, I realise that most of the posts I'm getting pings from I'm no longer interested in.
Having been over-enthusiastic at pressing buttons when I first joined, I followed many more posts than I really need to keep track of - more than 1,000 across the network I'd guess. Some I'd like to keep - about 100 here on meta, and a handful on other sites. Worldbuilding has 200 possible reasons to ping me, and I only really want about half a dozen. I'm fairly certain that I can't be alone in this.
Now, I can use the individual unfollow button from the activity page of the profile, this is fine for individual posts.
I'm not a coder, so I can't write a neat few lines to wipe the slate clean with any certainty it wouldn't delete my whole account or give me unicorn hoofprints over everything.
Could we have either (on a per-site basis):
An "unfollow all" button - with the traditional confirmation to prevent accidents.
An even better system of being able to select ones we want to keep, then invert the selection and delete those?
Related post regarding unfollowing all answers of a single question.