Tensioning pulley

Replacing compressor, need to pull off serpentine, some say I need to loosen retention nut others say not... when old pulley failed it just gave away, making me think I can pull tensioner without backing nut off. I only ask to avoid buying a tool retail I don’t need...
Never mind, done and done. YES you need to loosen retention bolt (unless the guy that replaced your serpentine forgot to tighten it) mystery solved!