Both practical AND gimmicky.

Aircraft components (the CH-46 helicopter, for instance has quite a few magnesium components) can be made strong and lighter than comparable aluminum assemblies. On the other hand magnesium is also more liable to corrode when exposed to maritime conditions (aircraft at sea and on ships).

My friend Larry "Bad News" B. was afloat on a Naval ROTC Cadet cruise the summer between his junior and senior years when a -46 crashed on the flight deck and burned. He has a melted magnesium blob that looks like a small pancake as a souvenir of that destroyed aircraft.