Why is it faster to use multiple files instead of one?

Question

For instance, header files in C++ are faster than having one main.cpp, and external css files are raster than inline/embedded.

Answer 1

Is it? I personally haven't read anything that says having separate files is faster. I also haven't read (or don't remember probably) anything that says it's slower either. Maybe post your source or the quote you found that says this.

Answer 2

~ swim ~ I can see how compilation could be interpreted as "slower", but they mention CSS files too.