Don't know, but I would guess that in most cases they want to coerce people into giving up their rights. I.e. "sign this to agree you give up your right to X". That might be remaining holiday pay or something else.

Actually... thinking back I've literally had an ex-boss in Japan try to get me to sign releases to various things. In the end I paid a lawyer to tell the guy to stop harassing me. This service would have been cheaper...