Shock collars are on the extreme end of positive punishment. They are intended to inflict pain to discourage a behavior. Just like any training tool, they can be used poorly. Using shock collar training without any clear direction will certainly break your dog. If you don’t shock the dog at the exact moment they do something you don’t like, you can send mixed signals discouraging the dog from doing something that is normal. Essentially traumatizing them from making a move. It can really knock the confidence right out of a dog.
I personally would never ever even think about using one, but dogs that benefit from shock training are typically strong willed and do not respond to treats, praise, positive reinforcement, etc. Your roommate should 100% train with positive reinforcement and ditch the collar.