In reply to Ahmad Awais.

@mark.k Ok retesting quickly on a site and the response from the XHR post that is triggered by keypress is a whole page on my installation with latest WP version using Chrome. The whole thing flashes with blue overlay on each key press and results in up to 83 requests and 233KB transfer can even result in MBs of transfer due to that. The main cause of MBs etc is the result of using tracking blocking plugin etc if you have WP Stats or Facebook etc things on your site.
All this is due to the full page response that triggers the redownloading etc of the site assets; scripts, style sheets.