Just saw this discussion. It's a safety matter and also an economical idea, to start engines only prior to taxi out. They sometimes use just one engine to taxi, instead of two to save fuel. I think all jet passenger aircraft have an extra engine for power supply, APU (auxillary power unit). This needs to run, if the airport can't provide an APU on a cart or underground supply of pressurized air and electricity. Small A/C like the J41 don't have an APU. But they have startes in the engine I guess, which allow them to startup the enginges without pressure air, like jet engines. Just checked some videos of Twin Otters in the Maledivan. They shut down the engines on the islands and start them without any power supply, after passengers have boarded. So for me, it's absolutely ok, to shut engines down for services. Some good FSX aircraft provide an APU simulation, to have power with main engines out.
Dan