CoA server conception

Greetings!  I am trying to understand the conception of coa server. What functionality does it brings ? Is it a some kind of proxy ? For example, I have a NAS server with configured coa port. I can send a disconnect request directly into it. If I configure a coa server on a freeradius server, will I be able to send a disconnect request to the freeradius instead and that is all? Thanks in advance for your answers! -- Best regards, Yuriy Ivkin