The idea is being raised on behalf of a partner. The idea is to combine the demand lines in the planning worksheet for the same item and create only 1 PO Line summing up the quantities for all demands. 

In a standard environment, this is not allowed because "The supply must fulfil the demand in quantity and date, the planning system balances supply and demand by suggesting actions to revise supply orders that aren't balanced. So, when one of the source demands is updated, the planning worksheet will generate a new suggestion to reschedule, cancel or change the Purchase Order line. However, if the Purchase Order line is grouped from different planning worksheet lines, it might affect the other demands."

The partner would like an option, where it is possible to combine demand lines and create one PO line.

We see value in providing such an option because that would allow customers who are generally raising POs where due to a combination of MOQ/Purchase discounts based on quantities/freight costs for their imported stock (majority of their purchases) might purchase 3 months' worth of stock at a time.