I understand about the whole

Blah.h
Code:
ifndef BLAH_H
#define BLAH_H


/* code*/

#endif
Then when you want to include Blah. you do:

Code:
#include "Blah.h"
So now you won't include the same file twice. But I was reading online and saw that it was better (faster compilation times) to do it this way. Something about the compiler lexical analyzer being the most expensive part of the compilation process (Sorry, I can't find the link anymore).

Code:
#ifndef BLAH_H
#include "Blah.h"
#endif
Where you want the Blah.h file included. Have you guys heard of this? If so, is it worth it to go through a project that takes 3-5 minutes to compile to change all of them?