Especially useful for single page applications but also if someone does not want to have piwik.php links in his page.
piwik.php redirects are currently used if a link goes to the same domain.
Maybe instead we could use the beacon trick? #6641
works only in Chrome so far I think... IMO piwik.php redirects should be disabled by default as it works for all sites and optionally users should be able to enable it in case they want it.