I used every bit of this, and every bit helped. It wasn't just a setting powder, it was a "settle down and stop wandering around my face" powder. A little went a very long way to hold my makeup.
Other people have noted that because it is white, it does make your skin look lighter, even chalky (I always have to wipe down my eyebrows after I use this). My foundation is a little dark for my skin so I didn't really mind, but once it actually sunk in it just turned out to be translucent. My foundation basically looks the same in the end.