Hi,

ARRIVAL transaction, which is used when inventory items are received, is not relying on pre posting for M1 or M10 postings to begin with. This means even though you set up M102 and pre post a inventory part line in purchase order, this will not be used in the financial transaction

If you look at the corresponding non-inventory transaction which is ARR-NON, M92 is relying on the pre posting to tell which code parts needs to be posted with values. 

I think, as this is not used anyway, there is no point of making it mandatory to define pre posting.

Why IFS is not using pre posting is another question. I think from a user point of view, we would know more about inventory parts (will be coming from engineering designs, will have product structures, we will know where they will be stored, where they will be applied etc) to decide which code parts- accounts, cost centres etc.- need to be affected. We would know less about non-inventory purchase parts, so its good to get a chance to point to code parts at the time of purchasing.

PR is a pre level of PO so I think it follows the same reasoning to not to use mandatory pre posting for inventory purchases.

Hope this helps

Thanks for your explanation