| If you press the pedal and the throttle moves to half way open this takes a certain time lets say 0.3 seconds .
With the booster fitted ;;the pedal pressed the same distance,the throttle still opens to half way open BUT it takes say 0.1 seconds . this gives better throttle response ,faster ,snappier,call it what you will.
As the throttle still opens to the half open position fuel cosumption is only affected during the time the throttle is opening and it is marginal.
The purpose of the booster is to give faster throttle reponse ,more in character with the car.
This may not be ideal for driving miss daisy ,I suppose the reverse could also be done so that it took forever to open the throttle to the commanded position ,but it would not be much fun to drive!
Imagine it took 3 seconds to open the throttle from the time you pressed the pedal ,now reverse that thought -thats what it does --respond faster
A | 
