Getting back to the original query, I would say yes, having manifold (non ported) vacuum advance at idle will (usually) result in a smoother idle and more efficient combustion at a leaner mixture saving fuel (but with higher NOx emmisions). Tradeoff is that if you like to stamp on the throttle at the lights you instantly have no vacuum, advance drops back to the static timing and feels like engine has bogged down and has no power
As
@dauphproto writes, his engines like a mechanical 28 Deg BTDC at peak torque (and zero vacuum).
Why is this so you ask? So as to develop its peak cylinder pressure at approx 15 Deg ATDC.
If his spark plugs ignited at 32 Deg BTDC then peak clinder pressure would be at 11 Deg ATDC and knock will occur.
At 24 Deg BTDC then peak clinder pressure would be at 19 Deg ATDC which is wasted Horsepower.
In the same way, if using just mechanical advance then as vacuum increases it takes longer to combust and peak cylinder pressure occurs after 15 Deg ATDC which again is wasted horsepower so vacuum advance is used to get peak pressure to occur earlier. At cruising speeds too much advance can be felt as 'surging'.