The Machine Gun is simple, but reliable. Its automatic fire is useful for keeping a stream of damage on an enemy. One of the base starting weapons.
Being one of the weakest weapons in the game in terms of damage and fire rate, there are cases where a Machine Gun beats the Nailgun and Shotgun with its range and accuracy, while being a hitscan weapon. It's easier to finish off a fleeing opponent low on health, regardless of champion use.
Like with all starting weapons, it's best to find a replacement as quickly as possible.