Use or don't use vacuum advance on distributor???????????????????

Vac advance= gas mileage.
If it cleans up anything below cruise by means of direct manifold vacuum...its because the tune sucks.

With guys running real high dynamics...that vac just does not drop off quick enough...the cylinder pressure catches the timing between vac adv and full mechanical and you get a nice lil clack/ping whe you dip the pedal hard.
It's all about what you're building imo, if its hp...plug the hose and walk away.