As far as I know, the BS prefix was invented to make it easrier for people to distinguish certain types of threads, just the same as lyr req, etc.

Complaints did contribute to the resons for a split which is optional for members. I still can't see why some object to it. The options in membership are:

BS filter: If "Yes," filters threads designated "BS / non-music" out of Threads listing.

Mix Music & Non-music: If "Yes," mixes music and non-music threads in the Threads listing.

It's a freedom of choice which way suits an individuals reading best, not an enforced option. Those that prefer it all in one list can have it that way.