I purchased the PAS option on the Boxster under the justification that one careless bumper scape might cost me the $2k that the system did, assuming a high insurance deductible. What actually happened surprised me. You can read my original review of the system here at the bottom of the OP.Adaptive cruise control with Porsche Active Safe (PAS)
Available as an option, this cruise control function regulates your speed according to the distance between your vehicle and the vehicle in front. A radar sensor monitors the road ahead up to a distance of 200 m. If you have set a cruising speed but have begun to gain on the vehicle in front because it is driving more slowly, this is detected by the radar sensor.
The system now reduces the speed of your vehicle at a maximum rate of 3.5 m/sec2 by restricting the throttle or by applying the brakes appropriate to the prevailing situation until the distance that you have preset is maintained. Your vehicle will now continue at a reduced speed. If the other vehicle decelerates further, adaptive cruise control will continue to reduce your cruising speed – even down to a halt.
For additional safety, if the system detects that the distance from the vehicle in front is decreasing, it will also prepare your vehicle for braking by precharging the braking system so that the brake pads are already in light contact with the brake discs. However, drivers still have to perform heavier braking themselves. As soon as the road ahead clears again, your vehicle will accelerate back up to the cruising speed originally set.
If your vehicle approaches the vehicle in front too quickly, Porsche Active Safe (PAS) will issue audible and visual warnings. In addition, the system briefly jerks the brakes and if necessary initiates target braking, with any braking pressure applied by the driver being increased within certain system limits.
A few months ago I was in stop and go traffic in California. In particular, this was a whipsaw kind of stop and go where it's 0-50 and 50-0 repeatedly within the same highway mile, 12+ lanes wide with long term construction projects in the area taking up the breakdown lanes. A benefit of PAS seemed to be that it handled crawling traffic well, taking some of the agony out of driving. You steer and it does the gas and brakes, like a partially autonomous vehicle. If the road is straight you're just along for the ride. Over time you begin to trust the system more and correct/override it less and less.
Current generation vehicle sensor and sonar systems can only detect objects directly in the path of the vehicle (front, front-left, front-right, and on some cars side lanes). They can't, for instance, anticipate a traffic pattern that a human easily can. For instance if the car in front of you is going 50 MPH but you see the car in front of it has stopped, you can anticipate that and slow down. PAS will attempt to fill the gap in traffic by accelerating up to the next car in front of you, and then slow down only when necessary.
It did the above flawlessly, realized it had gotten itself into some trouble, and did a panic stop without hitting the car in front me. Unfortunately for the millennial in the SUV behind me, she was not using PAS (or paying attention) and rear ended me at 5 MPH.
Technically I could have mitigated this in two ways within the bounds of the Porsche system - first by restricting the top speed of the PAS to perhaps 25 MPH. Second, I could have lengthened the following distance, though that is problematic in traffic where cars are cutting into each other's lanes. Of course I could have just driven the damn car myself and this may not have happened.
I kind of wish I had just gotten the Sport Chrono package in hindsight. Until the sensor can see through the glass of the car in front of you and "paint" then track every car on the road as a human's eyes can, these systems are merely aids. I would include Tesla, Audi, Mercedes, BMW and everyone else in this generalization. I do leave the system partially engaged to get crash warnings, but find myself not using it unless for actual 75 MPH highway cruise.