that is a very loaded question. basically, a single phase motor uses 2 lines of incoming power and a three phase motor uses 3 lines of incoming power.
a single phase motor is usually used for low horsepower applications where as 3 phase motors are used for larger horsepower applications.
"Right" is not the same as "Wise".
Don't step on my favorite part of the Constitution just to point out your favorite part.
Just because you can measure it, doesn't mean it is important. Just because you can't measure it, doesn't mean it isn't important.