What does machine equivalence mean and how can you make use of it?

What will be an ideal response?

Machine equivalence is the notion used in the rsh, rcp, and rlogin commands, which negates the
need to specify a username and password in order to perform an operation. By declaring a
machine equivalence, it is assumed that the same users and groups are defined on both machines
and that a user who is logged in on one machine is entitled to the same privileges on the other
machine. This enables the user to copy files and login from one machine to another without having
to provide a password, a convenience if allowed, but potentially a huge security hole if not
managed properly.