Distributor Recurving?

Vacuum advance can also cause issues with tuning/surging and promoting a lean condition if you aren't careful. Can it help with fuel economy, yes. I've had cars where the difference between with and without was less than 1 mpg. Worth the hassle, not to me. Depends on the build.

Then there is the whole manifold vs. ported vacuum source argument... Limiting total advance in the can if it's too much...

I don't generally put enough miles on my cars in a year to be concerned with the mileage difference, especially when the car requires a 50/50 or straight race gas for fuel.

Like anything, it takes work to get it right. Whether that effort is worth the benefit is solely up to the car owner.