Addy Osmani, Google Engineer, writing at Medium:

Tip: Preload resources you have high-confidence will be used in the current page. Prefetch resources likely to be used for future navigations across multiple navigation boundaries.

If you have a resource that’s on every page of the site (e.g. a logo) then preload is what keeps that resource from blinking from one page load to the next. Today I introduced a graphical logo to DrinkingCaffeine and preload does the trick; prefetch does not. At work we’ve experienced the same thing. It takes preload, not prefetch, to keep a resource perfectly smooth across multiple pages.