Every machine gun is for anti-personal use. It can't be pretty effective against armoured vehicles, can it? A coaxial machine gun is the one mounted at the turret, along the main gun.
Of course it is for anti-personnel use. It can also be used for reconnissance fire, aganist soft vehicles, etc. Most tanks had their sights graduated with two sight rings one for the cannon, one for the machine-gun. It is basically for any target appropriate to small arms caliber ammunition that cannot be engaged economically or realistically with the main gun.
