Wraps per inch?

I’ve noticed that sometimes yarn is discussed in terms of wraps per inch–I am just wondering if there is a greater advantage to doing this than to measuring it another way. Would you just wrap it around a knitting needle to get the WPI? Or does it matter.

Thanks!

You can wrap it around a needle, a pencil or a ruler (built in measure). Here’s a page with a chart at the bottom which may help determine weight - http://yarnforward.com/tension.html
I came across another chart but the text explanation with it is contradictory on most of the weights so I don’t know how standard the standards are.