Eh, I figured I'd address my thoughts on both as 'machine gun' has been used pretty much interchangeably throughout the thread so far. I've never heard of them referred to as machine guns since joining the Army, it's always either the designation or 'crew served' weapons. May just be my unit. Either way, I stand by my opinion.
For belt fed weapons, single shots aren't too hard to achieve. The 240B is quite easy to fire in single shots, but it is basically used to determine where your shots hit in relation to your sights. I can see that being used for a vehicle gunner to get used to the weapon so they can compensate. The slower the rate of fire, the easier it is to control how many rounds you send down range, of course. For belt fed weapons, not really needed, in my opinion. It would be neat to see a selector switch for rate of fire beyond adjusting the gas feed though.