What is significant about this sentence? The Quick Brown Fox Jumps Over the Lazy Dog

This sentence is significant because it uses each letter of the alphabet.

  this riddles' answer is library.

  the "leaves" are a reference to the books' pages that the library contains; the branches are a network of libraries that connect multiple libraries' collections, resources, and items in a system of a common database, integrating them; the branches' organization are a useful management tool for coordinating the multiple collections many libraries have.