Part 91 allows you to fly in VFR conditions that do not allow for control of the aircraft by reference to external references...for example...night offshore...no surface lights...overcast sky conditions (...say 10,000 overcast) visibility ten miles...(but no surface lights)...and being "VFR"...not much in the way of instrumentation required.
Before you squawk...that visiblity situation does not constitue a "weather" issue by definition under the FAR's.
Thus are you IFR...IMC...VFR...VMC or a combination?
