Often, the theft of a few dollars of materials (from, for example, a pad-mounted transformer) can cause environmental releases that cost tens of thousands of dollars to clean up! :-(
I assume you're referring to the old PCB coolant transformers which have been largely replaced with ones using ordinary mineral oil; of course by going back to the mineral oil we now experience some rather impressive explosions and fires when a transformer is ruptured by heat through short-circuit or lightning strike.