I've lowered many cars in the past, however, recently I haven't as I prefer keeping cars stock. However, the Model 3 just rides too high for a car of this class, this is particularly the case on the $70K+ Performance model which competes with a stable of very sexy looking vehicles. Previously as an owner of many super performance sedans like the BMW M3, ATSV, S4, S6, etc. the Model 3 Performance is just too high for this class.
Any Tesla representative should warn against lowering their car, any modification to a car's major mechanical or electrical components should be advised against. However, a 1-1.5" drop is very subtle for a car that already rides pretty high. Of course there is more risk to undercarriage damage, front bumper damage, etc. However, I feel the undercarriage on this car is already significantly higher than other cars in the segment including the Model S. The only thing I disagree with is curb rash. You're lowering the body of the car, not the wheels, that's a stupid comment, you'll have the same curb rash risk/damage regardless of springs.
This is the highest sedan I've ever owned. With a 1" drop, it will still have significantly more clearance than my ATS-V with Carbo Fiber package I just got rid of had. I treat my M3P+ as I do my previous ATS-V and BMW M3, an around town sports car. I won't take it off road, it won't see the snow, it won't go camping, we will use my wife's Volvo SUV for that stuff, so in my case the visual aesthetic appeal overcomes the reduced clearance. While negligible, the lower center of gravity probably gives some handling and extremely minor efficiency gains.
The PUP springs are already fairly stiff, much like other luxury sports cars in the segment. From my reading, most of the springs aim at lowering the car over improving performance, which is fine with me.