Do i save time when requesting page via ajax and excluding non ajax parts?

I am implementing page loading through ajax() and I would like to know if I can save some time when requesting a page through the jQuery function .get()

When running the .get() function I pass a parameter that will indicate to my PHP page that it is being requested by AJAX and that it should return only those parts that are marked as such.

For example, all my PHP pages have header and footer functions, so when these pages are called by my AJAX function, the header and footer functions will be skipped.

Will this save my any time and bandwidth in my .get() request and thus delivering the page faster? If not, is there any other way to accomplish this?