There's any number of ways I can find and filter files using the find command, and then with xargs I can pipe them all through a sequence of simple operations.
In a typical gui file manager that kind of stuff is just not possible. The possibility space for what you can do is limited by the visual abstractions the original designer came up with for file manipulation. With command line tools that space is virtually infinite.
Often we consider the command line to be for expert users, and consider it our job as system designers to hide it from the rest. But when you consider that most people are able to learn basic calculus at school, a skill that has practical use in real life in only a limited number of professions, why don't we teach people to use the gnu tools at school? A skill that would enable them to use computers in powerful ways for the rest of their lives?