I noticed the UFOpaedia article for machine guns states that "They are quite heavy though and have limited use other than suppressive fire". As far as I know there is no such thing as suppressive fire even in OXCE+, so this feels a bit like misinformation. Perhaps this line should simply read "They are quite heavy though and have limited use".
That said though, I wonder what suppressive fire in X-COM would look like? I'm thinking maybe a TU reduction for every projectile that passes within 1 tile of a unit, or maybe a penalty to Reactions for the turn, but without player feedback it doesn't seem too useful.