What happens if you don't rotate tires properly?

If you put radial tires in a position where they roll the opposite way there is a high chance of splitting belts. This is why rotating is of dubious benefit at best and should only be done by experts. I haven't rotated any of my tires in 40 years and I get Excellent tire wear.

I do not agree with the above answer. I have been rotating tires for over fifteen years. I always cross the direction of two of the tires. I have never seen that cause belts to slip. Every car and tire manufacturer recommends rotations to even out the tire wear.