It can be used to temporarily “burn off” a layer of fat in small areas. What happens is that about two millimeters of subcutaneous fat is mobilized in the area directly under the pads. You can compare this to the effect seen when shooting growth hormone, i.e., there’s local mobilization of the fat at the point of injection.
Much like high intensity weight training, EMS increases muscular density or “hardness”. Think of Ben Johnson. If you slapped him on the back you’d think you were hitting a brick wall. Although he had a great physique, he wasn’t “puffy” like Arnold Schwarzenegger ; he was as hard as a rock. So the thing to think about with EMS is density, not size. Think of it as maximal strength training and not hypertrophy training.