What are some advantages and disadvantages of allocating organisational rewards for staff bonuses on measurements using individual staff performance and group or team performance?

In process costing manufacturing environments where 'normal' spoilage occurs, the cost of the period 'spoilage' is treated as part of the cost of goods completed and transferred out during the period. Given it makes no difference to the accounting treatment, why do firms go to the trouble and expense of measuring the spoilage separately?