Manifold Vacuum Advance what am I not getting?

Since this thread is somewhat de-railed here's another example for MVA vs PVA...Maybe helps us understand the concepts?

340 @ 9.3 SCR (175psi cranking pressure) and XE262 cam running an OEM TQ.
Idle speed 825 with mixture screws 3 turns out 12.5 AFR
TCI 2600-2800 converter.
Engine seems to like 25* BTDC with a little effort cranking.

System set at 8* base plus 17* MVA plus 24* mechanical (starting at 1500 RPM).

What are the pros and cons of this set up as it relates to the MVA vs PVA? As with @340inabbody I'm trying to understand the concept.