I have been using stands for years. I have quality stands and I make sure they are placed properly. Two stands, or four stands, what is the difference?

As for the reason to have a car on four stands: 1) I had to pull the rear axle assembly on my 250SL, which meant I had to drop the exhaust system 2) for a full inspection of the undersides of the car 3) to rotate all four tires 4) to drain the transmission or rear axle - the car needs to be level for a full drain 5) to work on the driveshaft 6) to install a new exhaust 7) etc, etc.