NASCAR Racing: Why have a mirror where cars are closer than you think, convex mirror, many thanks

Question
Many auto side mirrors say "Cars may be closer than they appear"?

There must be some good thing that makes having such distortion. What is it?

Many thanks,

Steve  

Answer
The distortion is from having a convex mirror. The convex allows for a wider field of view, allowing you to see more of what's behind you. The bad part, it makes things look smaller, thus they look farther away although they are "closer than they appear".