Why use a “tpp” file when implementing templated functions and classes defined in a header?

Question

Please refer to the first answer in this question about implementing templates.

Specifically, take note of this quote

A common solution to thi

Answer 1

Files extensions are meaningless to the preprocessor; there's nothing sacred about .h either. It's just convention, so other programmers know and understand what the file contains.

The preprocessor will allow you to include any file into any translation unit (it's a very blunt tool). Extensions like that just help clarify what should be included where.