Why update pricing in two different areas?

When I am purchasing an item and the price is different than what is in the system, I was told to change the price in two different screens. The first area is the "Material Revaluation" screen and then update it in the "Item Master Data" screen.

1. Why does it need entering twice?

2. What does updating each screen effect?

3. Is there a special order in which they should be updated?

V2004A

Thanks,

Dave