Where it differs from rcp and scp is that it can be used to synchronize directory trees. Synchronizing means making one copy of a directory the same as a newer, modified copy of the same directory. rsync does this by copying only the changed portions of the files in the directory tree rather than by recopying the tree. This makes rsync very practical for use over slow moedm links.
This is useful if, for example, you do development or research work on both a laptop and a desktop computer and you regularly want to synchronize the directories on the two machines.
If you don't have backup hardware at home it can also be useful for maintaining a copy of your home computer's home directories in your CSE home directory--where it will get backed up automatically by us.
Note that rsync needs to be installed on both computers.
The second rsync copies newer files and changes from the local directory myhome to the computer mybox.
Both of these together synchronize changes in both directions.