I often warn new puppy owners not to let their puppy wear a collar if in a cage (say in the car) especially if it has a buckle and a tag on it. I am sure that a lot of people didn't heed the advice, or understand way, but to illustrate the dangers someone I know lost their dog because of this.
They had the dog in a cage in the back of the car, and crashed the car. The cage stopped the dog being hurled forwards into them, or the windscreen, and it stopped major injuries in that way. What it didn't stop was the collar catching on the side of the cage, the car ended up at a steep angle and the dog was strangled with its own collar before the driver and passenger recovered sufficiently to realise what what gong on.
A hard lesson....and these people were supposedly very experienced. Not something you consider but be careful. I have heard of similar tales with a puppy simply being left on its own in a crate.