What is the benefit of the Work Order under-completion tolerance in Process mfg?

Summary:

In Process mfg, the under-completion tolerance is on the batch quantity rather than the output quantity.

Content (required):

In Discrete mfg, where the WO output is tied directly to the completed quantity of the final Work Definition operation, there is obvious benefit for the under-completion tolerance. In Process, where the primary output is separate from the operation completion quantity, the benefit seems minimal. I can complete the full operation quantity at the last operation while reporting a much lesser quantity of the primary output using the Complete with Details step, and the WO will automatically complete without using an under-completion tolerance.