Turbolinks in prior versions of rails

Recently I have been reading about turbolinks which is deprecated but one should have a proper knowledge . I have read that turbolinks replaces the body of the requested page with the body of the current page and merges the head. The primary speed comes from not having to reload the assets like js or css files which are present in both heads of the requested and current page and are same. My confusion is some seniors say that turbolinks does not replaces the body rather it replaces the sections in the body. And If there is a full body swapping, then its almost same as even if you are sending a normal request instead of ajax. Now I am confused. Please give your expert opinion regarding the workflow of the turbolinks.