Called it once to get an ambulance for a family member. I can see why people in the States wouldn't use it for that considering how expensive it can be
A long time ago, my fiance at the time (my wife now) and I were in a play, and she slipped on something, fell and bumped her head a bit too hard. So, she was a bit dazed, but I was sitting with her. One of the theater managers called an ambulance to take her to the emergency room against her and my will. So, the ambulance came, and took her to the hospital. I followed in our car. She was in the ER for a total of twenty minutes before she was released with nothing wrong with her. There was no concussion like they had feared; she was just dazed.
The ambulance was not covered by our insurance, and ended up costing $1600 out of pocket. Not to mention the emergency room costs. Granted, some of it was covered by insurance, but not all of it. The total bill put us over $2000 in the hole. Lesson: Never call an ambulance unless you literally have a severe problem, and never call for someone else without their permission.