Posting a Purchase Order

I am very new to AX.  My company is using AX2009.  I was wondering if someone could tell me what the VendPurchOrderJour table is used for. I created a report using that table and then found that there was a lot of missing purchase orders in it.   My purchasing dept is creating purchase orders which they then receive and post the invoice but they are not always posting the purchase order and I was wondering what problems this might cause.

thank you for your help!