Before visitors click on a link, they hover over that link. Between these two events, 200 ms to 300 ms usually pass by. InstantClick makes use of that time to preload the page, so that the page is already there when you click.
If you want your website to not be flooded by requests, you can set a delay before preloading starts when users hover a link. It will still feel instant.
If you don’t want any wasted request, you may preload on mousedown.