FG 42 was basically used as a lighter alternative to the Machine Gun, since weight is a concern when you're jumping out of airplanes.
Indeed, from what I can tell, it's a BAR in many ways - both fired full-powered rifle rounds automatically, both were intended to be mobile automatic rifles, both used 20-round magazines (
), both suffered from control issues when fired fully-automatically that ultimately had them fail to achieve their intended purposes. Just the difference was one was heavier, giving it a weight problem but alleviating the control issues when fired from a static position, while the other had no weight issues but left its fully-automatic capabilities just plain poor.