A manufacturer may have raw materials/components that are phasing out and have a planned obsolescence date provided by the vendor. That may be in the near future, but also may be in the distant future. You would not want to block it for purchase since it is not yet at end of life (until the vendor planed date). Any purchase orders that you put in near the planned date would take that date into account so that orders placed within the timeframe + lead time would allow you to order. After the planned obsolescence date, trying to add it to the PO line would error out. It would be great to have:

1. A boolean field that you can toggle for planned obsolescence
2. A field for the planned obsolescence date
3. Code to move the purchases blocked boolean field to true once the date is reached.