If you are hanging cabinets (more than one in a row), then you need these!  These little clamps worked so slick to even things up and line them up.  There is even holes in the sides to guide a drill bit through the face frames nice and straight so there are no errors and end up blowing out the sides because you got too close with your hole.  Great idea that made my life much easier installing my cabinets.  Even my Dad, who has installed many cabinets over the years commented on how he wished he had a pair of these years ago, and trust me that says a lot.