If you use a computer every day, and the number of programs you use rises above about 100 or so, typing in a command to run a program is much quicker than choosing it from menus, so many developers choose to type commands for much of their work. This is roughly equivalent to using keyboard shortcuts on menus, but that doesn't work if you have over 100 menu entries, either.
Typing commands can be speeded up even more by using clever text interfaces. These allow you to use (say) the up arrow to go back to previously typed commands, and then the left and right arrows to move around and make small changes.