In a street car, you have to worry about speed bumps in the shopping mall parking lots. They are significantly higher than 1"! Then there is also the occasional debris that lands on the road you're traveling. Some of it can exceed 1"-4".
Yeah I don't know what his static height actually is, even if he really had 1" of clearance at full suspension compression his static would be at least an inch lower than I am with my car. And he didn't have an inch at full compression in the video I watched.
Granted the header flanges are basically a single point, it's not like the entire chassis is at 4" but that's about as low as I can manage with my car and still clear speed bumps in the parking lot without a ton of maneuvering. I ran my Challenger lower for a bit, had the header flanges down a bit below 3.5" to the ground at ride height. It doesn't sound like a big difference but that was basically the difference between dragging on every single speed bump and driveway apron or clearing the vast majority of it. Maybe a show car or weekend only car could pull it off but as a daily it was just too much of a pain in the ***.
Even as an autoX only car a lot of the parking lots and venues you use aren't actually all that smooth, you need to have some suspension travel.