I debated with myself over whether markers for traps were even necessary for Castle Meatgrinder. They are, after all, single events that can just be described as is. Either you find it and avoid it or trigger it, take HP damage, and then move on. Why waste time on a 3D terrain piece for something so transitory? Two reasons:
1. They look pretty cool. They help to make the 3D version of Castle Meatgrinder look as deadly in person as it does in your head.