vacuum advance

Are you sure it was originally manifold vacuum supplied. Most were venturi vacuum supplied.
When it comes to vacuum advance, The more I read the more confused I get.
Can manifold vacuum source be better than just disconnected ? Does manifold vacuum even drop enough to cause the advance servo to respond ?
Can I assume what works best for performance also reduces mpg ? I would forfiet a little mpg for better throttle responce and overall performance from a totally stock 2 brl. engine.