EDI Demand Management - ROI?

For those of you who have implemented EDI Demand Management, how has it saved your company money or cut costs? What reasons should I present to management to purchase this module? We would like a better process for handling blanket orders but are there other reasons to purchase this? I need to justify the expense. A brief overview or explanation of its use cases and abilities would be greatly appreciated too. Would it be possible to utilize this EDI for intercompany purposes? Such as automating SO/PO between our companies?