2 words:
tab completion I'm a lazy ***, so when i'm switching directories or installing using ./configure make bla bla i like being able to switch thru directories and stuff like that quickly, so there piggy, when you've loaded up a terminal you can just start typing something, and if installed in your system, like ehh, ahh, ummm. gedit or mozilla you can just type in moz and then hit tab, it will complete it for you or show everything that starts with moz...sweet huh?