Here's a quote from a posting on this forum:
For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively.
Read the full post "Timing and Vacuum Advance 101" here:
Distributor Tuning and Theory - Part 1
I was pondering this same question myself the other day and was searching the subject...