Say you want a shell on a box but you have to hop through another box to get it.
force@harold:~% ssh admin@maude
maude:~ force$ ssh root@whee
root@whee:~$ echo w00t
w00t
maude:~ force$ ssh root@whee
root@whee:~$ echo w00t
w00t
You can do that in one line using -t (pseudo-tty allocation).
force@harold:~% ssh -t admin@maude ssh root@whee
root@whee:~$ echo w00t
w00t
root@whee:~$ echo w00t
w00t
After playing with it, I can only get this to work for one hop. So yes, it’s of limited use. But I hop through another box every time I ssh at work, so I’m going to be getting a lot of mileage out of this little optimization. :)