Two HVAC units for large house

Some of my closest friends recently purchased a new house. I am very excited for them, because they are going to live a few streets away from me and my wife. The new house is really cool, because it is one of the only two story houses in this area. When the two-story house was built 50 years ago, one of the latest and greatest architects designed this specific house. The architect was wonderful friends with a doctor in the area, and the two-story house was designed as a favor to the doctor. When the doctor retired from working at the hospital, he decided to place the large house on the market. My friends were excited to see the house. We decided to accompany them to the showing. The realtor was very nice and accommodating. She met all of us in the parking area, at the same time. One thing that caught my attention was the two HVAC units. Each level of the house has its own HVAC unit. The downstairs thermostat is located in the kitchen. That thermostat controls the temperature settings for the HVAC unit that is located in the garage. There is an additional HVAC unit located above the garage, and this is the machine that controls the heating and cooling for the upstairs areas. The thermostat for the upstairs HVAC unit is located in the hallway, next to the bathroom. The second story bathroom is bigger than my master bedroom. I think my friends will probably spend a fortune to run both of these HVAC units, but the house is too amazing to let go.