You may need to connect to a remote location via SSH, but if the remote location doesn’t provide an interactive shell, the connection is most likely to drop.
For example, you may need to port forward from the remote connection’s port 9001 to localhost’s port 6000, but the remote server does not offer an interactive shell.
To prevent a disconnection, use the -N flag:
$ ssh -N -L 9001:localhost:6000 user@remotehost
-N option prevents remote commands from executing, and therefore allows local port forwarding.