I'm running distributorless system so I'm out of the picture here but I'm able to control engine load advance with TPS. At very low load state at steady speed (=max vacuum), my engine is happy with 48°. At 130kph (80mph), I really have to feather the gas pedal to keep the car steady whereas before it would need way more gas pedal travel. So to the very post, I can say: Yes, you can increase fuel economy by controlling vacuum advance (by 20 to 30%) When fuel mix is low (low load, low throttle angle), cylinders are not full, gas mix is much slower to burn than at WOT. 2 options exist to get good burn then: you ignite the mix exactly when needed - not possible without load advance control - or you increase the volume of fuel mix. With "poor" (= no load/vacuum control) timing management, you can only use the 2nd solution which is the less efficient. By controlling load advance, you also improve acceleration/transition. Engine is running in a way more efficient state, transition can be done with efficient mix ("easily" done with DCOE by playing with idle jets) but also efficient advance (going in my case from 48° to 34°). Car is much more responsive as it has ever been when I was running Unilite dizzy without any load control. here's a very good article about fuel economy, advance load control & DCOE