I did one of these at Sebring in the spring. It's a lot of computer car, with a bit of lead-follow mixed in. We didn't get around to fooling with setup changes, which was fine with me since I was running in a regional group that weekend, and wouldn't have been able to use anything I learned about setup for the races.
In some ways this was a lot like the old computer car program, where you'd sign up to do an entire day in the car, versus the current system where you sign up for a single data collection. I did the old program a few times back in the mid-90s, and while I always found the data about where I was losing my time on the track quite interesting, I was rarely able to go any faster despite a clearer understanding of my weaknesses.
Interestingly enough, this time around I was able to make some improvements based on the computer feedback. . . . I guess some additional years of experience under my belt helped. I also found one other thing
extremely helpful -- if you get the computer car dashboard display set in the right mode, one of the digital readouts captures your lowest speed during each corner, and retains that number until you get to the next corner. Although the readout occasionally gets messed up by locked brakes or corner exit wheel spin, for the most part it gives a very clear view of how well you've optimized your corner entry speed --an area that always gives me trouble. It was not unusual for me to see 3-5 MPH variations in entry speed on any given corner from lap to lap, with no appreciable change in RPM at track out, and it was instructive to get that feedback instantly, when I still remembered quite clearly what I had just done on the corner in question. And there where also a few occasions when I saw a huge jump in the minimum speed, but then a big loss of RPM at track out --obviously a case of trying too hard. Quite frankly, I would kill to have this display available each and every time I'm in the car. Surprisingly enough, not all of the computer car instructors know about this mode, so make sure to talk to someone like Phil or Gerardo, who can show you how to pull up the display in question. While the minimum speed indicator can be useful in the normal single-shot computer car session, you don't really have time to figure out your baseline minimum speed, and then try all sorts of different things to improve the numbers at each corner, before you run out of laps. In contrast, the test day format gave me plenty of time to experiment with ways to up the entry speed numbers.
Hard to say whether a test day beats out a day of lead-follow with JP. Both are helpful, each with their particular advantages. Wish I had the money to do BOTH every weekend, but that won't happen until I win the lottery.
As an interesting aside, I have a theory that one thing that sets the really talented drivers apart from us mere mortals is an almost exquisite ability to sense their actual speed -down to fractions of a MPH-- at any time, without the need to look at a speedometer, tach, or other instrument. If you have that ability, then you are going to be able to judge quite accurately whether your corner entry speed was a bit better or worse on any given lap than on any other, and this will allow you to quickly identify what corner entry technique works the best, no minimum speed readout on the dashboard required. In my case, however, I find that within a 3-5 MPH range, I can't really judge on any given lap whether I was on the high end or the low end of the range, and thus I need the minimum speed dashboard readout to tell me whether I did the corner right or wrong. I've tried in my road car to develop this skill by guessing my speed, and then looking at my speedometer to see how fast I'm really going, but find that I am perpetually thrown off a bit by the nature of the surrounding scenery . . . i.e. if I'm on a wide open road, 40 MPH feels a LOT slower than if I'm doing the same speed in a narrow alley, and with the constantly changing sight picture, I'm only able to judge my speed consistently to within + or - 5 MPH of my actual at any given time. I think perfect perception of speed must be to a racing driver what perfect pitch is to a musician.