Therapy animals save lives.
These dogs are even still so much more amazing. They check rooms before their handler enters, so they can clear it to help the person feel safe. Like in the gif, they are there when panic attacks or nightmares occur, to be something for the person to help ground themselves on, or yes just to turn on the lights. Even more amazing, many people are able to reduce their medication when they have a PTSD service dog there to help them. These dogs are useful for not just veterans, but also victims of abuse, accident trauma, natural disasters, and others. Their training allows them to be useful in situations where medical assistance is needed, as well. Some PTSD dogs are trained to recognize repetitive behaviours in handlers, and signal the handler to break the repetition and stopping the behaviour and possibly injury.
Service dogs in general are just awesome. Remember to respect any that you see out in public. They are not there for you to walk up to and play with, even the puppies!