The MG's are supposed to be used in squads. An MG puts down surpression fire on a target and the rest of the squad directs their fire/assault to the target that is under fire. Half the time the MG kills the target. The rest of the time, if done properly, the MG will force the target to not be able to effectively return fire and the rest of the squad can easily get him. MG's should always be kept at a distance.
These were the tactics used by all sides in WWII. Each squad of soldiers had at least 1 LMG or MMG and it was used for supression/covering fire. It's still done today.
This is not how the MG's are used by people in the game. Most lone-wolf it and setup on the flanks without much support. They basically become rifle-bait. Teamwork is key to a MG's survival and success, as it is for any class in this game.
Oh and anyone that says the 42 is too inaccurate or the spread is too much, you're using too long of bursts.