Structural building designs, flooring, technology, crafting...
Almost everywhere you go, you'll see a square shape. It might be there for MANY reasons. It's used in architecture to give it a "balanced" shape, so that no one side seems shorter or longer than the rest. It can be used with making floor tiles, which is basically design. There's so many uses for it in technology that I can't even name one off the top of my head, and squares make excellent shapes and figures for crafting certain things.
Edit: There's many more uses for it than the four examples I provided. Those were to just give you a general idea of the importance of a square.
