Hi dave the great thing about a dyno tune is the results are instant, first power up the car this tells not just the hp but how lean or rich she's running can also up timing or bring down timing what ever the car likes ,this can be done without putting everything back together every time you make a change and risk losing your licence giving it a hit on the test drives.
ive seen plenty of cars pick up 30 plus hp @ the wheels from bad afr's and not enough or to much timing.
cheers chris.