Making more of a product than you are selling at any point in time, or, making them before you have received any orders for them can lead to a waste of time and money.
TIP: If you can, make your items to order. When there is a lull in demand, take the time to complete other tasks. This could be training new staff, assembling cardboard boxes, maintaining machinery, or any other task that could not be done while your business is producing at full capacity.
Signet customer and WA local, Murchison River Swags, hand-make their swags to order to avoid cost and time wastes associated with over-production.