I notice purchase orders do not seem to tie to much. 

• If I enter a scheduled date, it seems to do nothing.  I use the scheduled date of a purchase order to get an idea when the invoice will arrive to forecast Cash flow.
• If I enter a Delivery date, it shows up on the purchase order and indicates the scheduled date to the Vendor.  However, it hasn't been delivered!  

So what is the purpose of Scheduled Date and Delivered Date?

It seems sensible the Scheduled Date should show up on the Purchase Order for the Vendor.  If tied to a task, the scheduled date could be updated in accordance to changes in the schedule. A memo could be sent to the Vendor indicating the updated information.

This year we have had many items backordered for months.  Cabinets may be delayed for three months.  By updating the scheduled Delivery it can also update the schedule for the Granite countertop installers, for example. 

The Delivered Date should indicate the Purchase Order has been at least partially delivered on a specific date.  If the Order has been fulfilled it would automatically close.

I don't understand what the Delivery date is for.  It indicates to the Vendor when delivery is expected but I consider that a scheduled date.  What do either of these tie to?

If I have  Purchase Order it should tie to committed costs as the PO is a commitment.  Possibly the cost report could indicate which costs are committed but not yet invoiced.  For example a column for "Costs", and another for "Committed" and a total "Estimated Costs to Date."