You can often use manifold vacuum to offset the the retarded initial timing on CAP/CAS set up. Its a lot simpler for many people than correcting the advance curve.
However, since this thread is about myths, its a myth that ported vacuum has anything to do with emissions.
This is a big myth, and I beleived it too until a couple of old time tuners set me straight.
Then I started looking at stuff written and built at the time - particularly Chrysler stuff.
1959
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from 1959 page 10 (Session 136) of the Chrysler MTSC.
It did not change a decade later either.
1969
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from 1969 Ignition System Analysis (Session 259), Master Technician's Service Conference
Go look through shop manuals, the MTSC, at photos and surviving example and it will be interesting to find what year or years Chrysler first used a vac source above the closed idle position.