Using .php for a file extension allows for all HTML, CSS, JS, and PHP content, etc., while .html does not allow PHP code to be read by the server-side engine.
As a rule of thumb I just use .php for my files even if I have no PHP code in them.
So… Is there ever a time when, for some reason, one ought to use .html specifically? Perhaps search engines index the file differently/better or it loads faster or something? But as of now I see no reason to do so, even with a file that has no PHP content.
Apparently no one is understanding the question:
Does it make any difference at all if I save a file as .html over .php when I have no PHP content? Shouldn’t there be some difference? The file is clearly a different entity when saved with a different extension.
When you give a plain HTML file a .php extension, it causes the PHP engine to parse it. While the performance hit is negligible, it’s still an unnecessary waste of resources and a best practice would be to avoid it by giving your non php pages an extension of html.