At the moment Cash Flow Forecast includes only purchase orders and posted purchase invoices (vendor ledger entries), but not non-posted purchase invoices. In many cases companies can have up to hundreds unposted so called cost invoices, which are not based on purchase orders and total amount of these invoices can be very significant in terms of cash flow.
This is becoming more and more important, because BC's own tools for purchase invoice approval process is developing rapidly (power apps/power automate) and specially if integrated third party ISV solution (e.g. ExFlow) is in use.
It would be very usefull if in Cash Flow Suggest Worksheet Lines request page includes option for purchase invoices and PI's would be taken into account when calculating cash flow forecast. Purchase orders and purchase invoices are even in the same table, both at header and line level.
At the sales side this is not so important in cash flow sense, because usually sales orders are invoiced rapidly after delivery.
Of course, cash flow date should be based on promised delivery date, if based header level information or on planned shipment/delivery date, if based sales order line level.