Total weight is crucial for how far a plane can fly. So - Pilot weight + Payload weight needs to be considered.
In terms of damage, if you hit the right spot without redundancies you can shut down or severely limit operations of a plant even with only a small material damage. Even if there is no visible damage, reducing the structural integrity of pressure pipes and the like can force a shutdown of that equipment until the damage is properly investigated.
In 2019 Houthis successfully attacked two Saudi refineries with a small swarm of drones, forcing a shutdown.