Ok, so this is bordering on religion, but there is not always an opportunity to use X (old Windows box, Wyse / Dec terminals, etc). I may be approaching the "old enough not to be trusted" crowd, but after 10+ years of sysadmin, a good command line or curses / screen based interface can be many times less stressful on the machine, network, or other resources.

It all depends on the needs of the application.