One that has come in handy a few times: When a machine is so starved for resources that it can't even allocate a pts for you, but you want to run some forensics, use `-T`:

    $ ssh -T user@host <command>

Even if you're plumb out of file descriptors for example, you can run...

    $ ssh -T user@host lsof

...or whatever, and get your command output dumped to the screen, even if you don't get the niceties of a terminal.