Detach and reattach to processes in a console environment with Screen.
Imagine for a minute you are connected to a remote server, running a crucial job and your link goes down. Your job will most likely die with your session. If you were running Screen, your job would have continued and you could re-attach when your link came back up.
Now imagine you are on dial-up (some of us still are!) and you are connected to a remote server, and need another session – say you want to su but still access both sessions. Instead of connecting a new session (and wasting more precious bandwidth), you could simply open another ‘window’, run your commands in there, then switch back and forth as required. Following on from my previous example, you could then start a job, detach, then re-attach later on.