Comment from .php programmer - opinions?

Okay, I'm so new (and so confused yet!) to .php, that I wondered what all of you with so much more experience think of this comment from the who wrote the book I'm studying from:

I may be reaching here but the point I think he is trying to get accross is that if you have PHP configured to parse files with the .HTML extension and execute any code it finds in those files, then PHP will look at every HTML file that is being requested regardless of whether it has PHP code in it or not and try and execute the code in it. No php code, no execution, but you are still using the php engine to parse the file prior to sending it to the requesting client. This is inefficient due to the fact that the engine is parsing files that do not need to be parsed. For example, if you had a site with 100 .html pages, three of which had PHP embedded in them, instead of PHP only being called to action when looking at the files that contain PHP code, it is called into action for all 100 pages 97 of which do not need to be parsed by php. Hope that makes sense.

Thanks blindeddie - I think I get the idea. But then does he mean when you include .php in an HTML page? (by the way, he wasn't talking to me - I don't even know how to make pages with both .php and html yet...sigh) Or am I getting too far ahead of myself here? (Shoot, I didn't even know such a thing as .phtml existed!)