disabling a node in F5

If someone is taking down a server that is on the LBs....what's the purpose of disabling the node in f5 before they shut down the server? If they're already shutting it down, won't the lb just say it's off, then when they bring the server back online, the lb will know and say it's on. doesen't this all happen dynamically? I've been asked to force offline the server(node) from the LB before they shut it down...but idk why exactly i'm doing that or what's the purpose... thank you