I play the clarinet and I taught myself circular breathing for one particular piece. I can guarantee you it is not a standard technique. It’s not even something that you can expect a professional player to be able to perform. I think I’ve only ever seen one performer use it.

It can be handy as an option for long fast passages, to avoid needing to sneak in a breath. Much less useful for holding a single long note, because it’ll impact your embouchure and put a hitch in the note that can be disguised between notes in a faster passage.