Distributor Vacuum Advance?

Interesting question. Sounds right re the mechanical advance being set up / not needing vacuum advance. We have an essentially stock 74 440 car and I run it with out vacuum advance as well.. Seemed generally to run worse with the vacuum advance hooked up and I have messed with the timing considerably while experimenting with vacuum ports on the carb. I need some timing tape on my harmonic balancer so I can see what is happening with the mechanical advance on that car... dangit.. Its like, depending on where the hose is hooked on the carb or manifold, it creates different timing characteristics. I have never heard nor understood the entire theory on vacuum advance or retard. Some say if you have a constant source of vacuum on the distributor then you can get a retard effect during full throttle acceleration which would help reduce detonation but during cruise you could have the full timing helping mileage and torque.
I bet slantsixdan would be able to add some solid clear explanation to the subject..