on a lot of cars with no pan all the belts have covers. on many t4's there is no plastic covers apart from the cam belt. the power steering, alternator etc all sit low on the engine, close to the road. it would only need a scrap can or sharp rock to jump up into a belt get sucked into the cam belt cover and bang goes the engine. if a cam belt snaps while on the move you might as well scrap the motor. it would cost more to fix than buy a new one. but then, my brother drives a slammed golf with no pan and hasn't had a problem. just watch out for sharp objects in the road!
a pan keeps the bay clean to.