In the "Connections" tab in Server Properties, there is a checkbox for
"Allow other SQL Servers to connect remotely to this SQL Server using RPC".

What exactly does this do?

I unchecked it on one server and re-started the MSSQLServer service to make
setting effective.

Next, I went to a different server and promptly registered the first server
where I made the setting without any difficulty. I was hoping to not be
allowed to do this because of the setting change that I made. Can anyone
explain? Thanks. Chuck