In my opinion, there is no reason for 20" wheels on any roadgoing vehicle smaller than a semi. Tires and wheels cost a lot more, tire/wheel combo is heavier, ride is usually worse, and the lower sidewalls make for easier wheel damage.

It's just a ploy to make cars look more like the sketches from auto design school with no practical reason at all. It's for people who buy vehicles to "wear", not drive. Like 6" high heels with huge platforms on women's shoes.

George