I guess in the same way as with subscribing to a RSS feed or E-Mail Newsletter.
Are you aware that “All” is only a small part of the fediverse which someone else on your server subscribed to already? There are still many other unknown unknowns which you will never find via “All”. You have to find a way to find those anyway.
I understand looking at “All” now and then to see what others on the server are subscribing to, but it won’t find all unknown unknowns.
edit: Therefor doing all the work in blocking things seems to me like unnecessary work if you only seldom go to “All” while relying on “Subscribed” for the normal functionality.