Vastly improves every day drivability. Once you hit vacuum under acceleration, the whipple (without SmoothBoost) kicks in at it's maximum boost, whatever your setup is running. So, even if you just want to give it a little gas, if you hit vacuum, you're at 9 lbs. of boost. With a SmoothBoost, your boost is linear with the position of your gas pedal. So, you can give it a little gas to pass grandma in the Hyundai, and you will only see 1 to 2 lbs. of boost. The only way you get maximum boost is at wide open throttle.
I actually did not enjoy driving My truck before I installed the SmoothBoost. Now, it's a blast.