Brent Sordyl's blog

Feature flags and flippers mean we don’t have to do merges, and that all code (no matter how far it is from being released) is integrated as soon as it is committed. Deploys become smaller and more frequent; this leads to bugs that are easier to fix, since we can catch them earlier and the amount of changed code is minimized.

This style of development isn’t all rainbows and sunshine. We have to restrict it to the development team because occasionally things go horribly wrong; it’s easy to imagine code that’s in development going awry and corrupting all your data. Also, after launching a feature, we have to go back in the code base and remove the old version (maintaining separate versions of all features on Flickr would be a nightmare). But overall, we find it helps us develop new features faster and with fewer bugs.
(Link: Flickr Developer Blog » Flipping Out)