OK if I speak for the loyal opposition?
Carb tuning and ignition advance are "inextricably" (50 cent word) tied together. It makes for all of the differences in experience we share when working our way through a tuning problem.
My usual mode of operation - and Ted relates it well above - is to recurve the distributor's mechanical advance curve. It involves adding initial advance - and reducing the centrifugal. Obeying an upper combined mechanical advance limit that has to do with fuel, compression ratio, and exhaust capability. This is done with no vacuum advance what-so-ever. It is the tuning I want for a "contest of speed" - providing all of the bottom end I can get - and no knocking at the top end. I put the curve into the distributor - and go about tuning the carb from there. When accelerating the the engine at WOT, I want the best combination of advance and fuel mixture I can get.
To drive this tuning on the street -the driveability of the set-up has to be evaluated - will it re-start well at operating temp? - does it overheat when idling in traffic? - does it gobble fuel like no tomorrow? -plenty more to consider than flat out power production. Vacuum advance can alter the "pure power" tuning to something more drivable - "automatically" - by using engine vacuum to determine whether you have asked the motor for power - or economy.
My experience - has shown me that low initial advance timing numbers - like the 3°-6° called for with these mid -fifties Fords (stock with no modification of their centrifugal advance mechanism) - puts a lot of unburned (unleaded alcohol laced) fuel in the exhaust manifolds or headers and burns it there. Makes them idle hot. Ported vacuum will let these "factory timed" engines sit there and cook with a tank full of crummy fuel - and we all buy it at some time or another - or let the vehicle sit long enough for it to get bad. Re-curving the distributor to provide 10°-12°-14° initial advance - and limiting the total to suit on the top end - will help this situation. But....I don't think its enough. And as the initial increases - I see (and hear of) more instances where the engines don't start well hot.
So I tune mine by setting up the curve, tuning the fuel curve of the carb - and then adjusting the vacuum pot to provide some additional advance at cruise vacuum. Only enough to do some good for economy - and keep the part throttle knocks away. When this small amount of vacuum advance is stacked on to the initial - at idle with live manifold vacuum - the exhaust manifolds cool down a bit and the water temperature drops as well. When you floor it - the system behaves exactly like the ported arrangement - she shifts to the mechanical curve and away we go.
Ted's point about what happens when the throttle snaps shut - and the manifold vacuum driven advance can delivers all it can add as the engine tries to drop rev's as quickly as possible - has not caused me a problem (instantaneous knocking), when the engine is set-up with the modified advance curve. The engine is absorbing power - not delivering it - and that is all the difference. I have found it to be advantageous to orfice the vacuum line and dampen rapid movements of the "point plate" in the distributor so it isn't jerked around - but no evidence of preignition. Be aware ......a higher compression engine might behave differently and mine is not "optimized".
Steve Metzger Tucson, Arizona