Well basically it gives you the bell curve of salary range. That's a pretty good range to go by. The thing your trying to figure out is where you fall in that range. You can be anywhere in that range based on your idiocy, or whether you have a moleh moleh moleh moleh on your face. Just depends. (yeah i know bad austin powers joke)
Remember if you look at janitorial pay in redmond seattle the low range could be in the mcdonalds, and the high range could be at microsoft. The company matters too.