Well over half of my inspections are foreclosed properties. I always ask to have the utilities turned on for the inspection. Most of the time the gas and electric are on but the property is winterized and the water is off at the meter.
I have a small diaphragm compressor that I connect to the hot water laundry connection or the water heater drain so I can isolate hot from cold during the test. I check all fixtures for leaks. I have been doing this since the last early 90's and find most leaks.
As for the water heater, I test fire it and turn it back off after checking for drafting. I have never burnt out a water heater doing this.
The time to do this is procedure minimal for most homes. There are always a few that cause problems and I recommend a plumber be hired if I can't locate the problem.
In the Denver Metro area, most buyers are having the sanitary drains scoped for around $100. I am toying with the idea of buying the equipment and offering the scope with the inspection for an additional fee.