Because some people prefer using the keyboard instead of the mouse.
Shortcut keys
shortcut key
At right side of the keyboard there are shortcut keys. They are are used by right fingers.
it is referred as a keyboard shortcut
Yes. You can do the necessary things with the keyboard quite easily. Once you know the various shortcut keys and function keys, it is easy to do. A lot of the shortcut keys, like Ctrl-C for copying, are the same for different applications, so you don't have to use and remember different ones for each application. So it is well worthwhile learning and using the different ways of doing things with the keyboard, even if your mouse is working perfectly. With a little practice you will be able to do things just as quickly with the keyboard or mouse.
Shortcut
Shortcut keys
Shortcut keys
Shortcut Keys
shortcut key
Shortcut keys
http://www.cookco.us/technology/shortcut_keys.htm