C++ functions do not read input from the user and do not 'print' information onto the computer screen.

Question

Why is this recommended?

Answer 1

It was likely recommended by someone very proud of their knowledge of semantics. A 'function' is not supposed to have side effects, such as changing the state of variables outside the scope of the function, or outputting to the screen.

In technical terms, it doesn't really matter... the code will still run.