In event that a vehicle that has a weapon mounted top outside of the vehicle but the weapon is buttoned up. If a non crew could man the top mounted weapon this would be useful. Not all tanks etc. have top mounted machine guns etc… but if there were vehicle mounted machine guns, crew served weapons etc… the ability to not only ride a vehicle but also crew its weapon would provide more than fix mount machine guns or provide even more fire for things like armored cars and tank crews how may not normally crew, or are short crew. I think you can already tank is abandoned but crewing an uncrewed outside weapon or vehicle.
In this same vein being able to select destination for vehicle and riding shotgun would be useful firing out of vehicles might add to the armored combat element for Tunisia etc… Anyway just a thought. The ability disable these weapons on enemy vehicles would be useful.