c++ - including .h files -

Suppose I have two .h files: AH and B.H. In addition, AH includes BH:

BH - Defines class B.

  square b {...};  

ah - defines class A, which uses class B.

  # # # # # # # # # #; B); };  

Now, I have something CPP file, which is A and B classes (B class is not used only in A: some functions (B))

From the perspective of design-pattern and coding style both ah and ari What are the pluses to include?