This is a mechanical form of exfoliating the skin. Typically each unit consists of a compressor and a low pressure action pump, which delivers a controlled amount of crystals to gently abrade the superficial layer of the skin. Alternatively there are some modalities that use diamond heads to have the same effect.
In my experience it can be over-used and over-promoted; it effectively has a superficial brillo pad-like effect on the skin. I would typically only recommend it in conjunction with another machine or treatment such as a peel, or a galvanic treatment where the exfoliated nature of the skin is then used to its advantage. I would personally opt for a light peel and meso in the place of this machine.