It lets you manage shape keys by bulk; you can move, rename, delete, and apply dozens of shape keys with a couple of clicks. 

When I say 'apply' I refer to "Create shape key from mix" with just one shape key being mixed at a time. For example, if you have shapekeys that have keyframes and/or blends (with vertex groups) and you want to create new shape keys that when their value equals 1 they'll get to be like this original values' keyframed value for a list of shape keys without combining them. This is useful for example when creating variations of shake keys.