Here's another reason why I like raising the car in the air with three support points instead of four:
As most people know, if you put (for example) a four-legged stool/chair on an uneven floor, the stool/chair rocks because one of the four legs isn't touching the floor. Use a three-legged stool, on the other hand, and all three legs will touch the floor, even if the floor is uneven.
My garage floor and driveway are not perfectly flat. I'm guessing this is true for most people. If I try supporting my car using all four pinch welds, it stands to reason that only three of the pinch welds are holding the load, and one pinch weld is probably floating above the jack stand (or nearly floating, without holding its fair share of the car's weight). By using my three-point support method, I know all three points are distributing the car's load appropriately.
So I don't like the process of getting the car up onto all four pinch welds. But I also don't like the way the car's weight would be distributed to those four pinch welds after the car was fully raised above an uneven surface.