It really depends. If it is a car with a new combo we have to run the dyno as we need to make sure it is safe AF wise, voltage etc. A example was last week we had a 70 Chevelle SS LS6 the customer wanted to just rent the dyno, we had him sign a release/waiver. We ran the software he drove the car on the dyno. 99.9% of the time we run the dyno and the car, but every now and then you get a picky customer with a old muscle car who wants to run the car on the rollers. Good question