Hi Ali,
I see this blog post in relation to that parameter:
I think it says that AX will set the sales/purchases prices based on the cost price when the order is created. Since your item is costed using weighted average, the cost can change when you run inventory close. The blog post says the price on the sales and purchase orders will be updated, unless the intercompany sales order is invoiced - in which case neither price will be updated.
That doesn't make complete sense to me, since inventory close normally ignores sales orders unless they are invoiced!