The PW screen forms part of the AutostockR routine, basically under HOST there is something called PRODSOM, from PRODSOM you can access the PM (Promotions Management) screen, from there there are the PL, PI and PW screens.
I know the PL screens are supposed to be done on wednesday, for promotions starting in two weeks, so basically you see what is coming up on special in two weeks, how much you save, how much this item sold previously on different promotions, and basically tell AutostockR how much you think your Promotional Uplift will be, and whether you want any stock for Bulk Displays.
PW screens on the other hand are used to manage promotions in the CURRENT week for delivery on later loads, so you can edit stuff you did in your PL screens (e.g. say Benson and Hedges Smooth arent selling as well as you thought, so you can downgrade the store demand - or increase it if it's selling better)
Never quite sure what the PI screen is for.
edit: i think i've got it the right way round with PI and PL