The telescopic sight on the MG 42 mounts does two things: it enables the number one on the gun to keep an extremely low-profile, even to remain completely behind cover.
It also helps the number one to see the target. The fact that it is an area weapon is irrelevant to this. This is why telescopic sights have been used on machine guns ever since the First World War, and are being used extremely frequently in Iraq and Afghanistan at the moment.