Graphical User Interface
(GUI) a human-computer interface used by controlling visual image representations of digital objects, often with a pointer or touchscreen
Command Line Interface
(CLI) a human-computer interface used by typing commands into a terminal
Being accustomed to only interacting with computers using GUIs will make most wonder why anyone would use the command line. After all, nearly all modern tasks, even software development ones, can be done with a GUI. GUIs enable unexperienced users to be able to do complex computing tasks intuitively.
What the command line has that most GUIs don't is
Command Line interfaces are often preferred for their physical ergonomics. This lowers physical requirements that control how the computer can be used. Because the user does not need the mouse, they can use the computer in more confined spaces, save time not moving their hand to the mouse.
More importantly, the command line makes your workflow more ergonomic. Files with known locations can be accessed in a single action. Total customization allows you to automate common tasks and modify tools to fit the tasks for which they are used.
These ergonomics move the computer interaction process closer to pure thought. Without distractions, command line interface users will not only be able to act more directly, but think more directly.