A few weeks ago while trying to move a picture I accidentally dropped it, busting the glass and splitting one of the corners. It also left a gouge in the hardwood floor but I try not to think about that.
So the Mrs finally prompted me to get the picture fixed. First I had to remove the backing and all the staples holding the picture in. Then I carefully removed all the shards of glass. So now the frame was ready to be glued back together but corners, especially with moulding, can be difficult to clamp. That's where this fancy little doodad comes in handy. 
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I believe it really is a corner clamp. Whatever it's real name, it worked great. A couple hours later I was waiting at the hardware store for a new piece of glass to be cut and installed. It was rainy so there were several men hanging around, just chatting. Hopefully now I can get the picture back on the wall without breaking it again :)