@b0rk (I am in the 15+ years command line user group now, but anyways):

- batch processing tools - for me this was the "rename" tool for renaming a lot of files at once. This would be very long and error prone to do with a GUI filemanager, so it was worth the time learning a command line tool
- making yourself comfortable: there is a lot of configuration and settings, and a few changes can make a huge difference! (for me, it's making my prompt red when a command errors, and green otherwise)