Starting with a customer order is like pulling on the noodle. We start with the sales order, and then move along the rest of our process to follow the order and keep the noodle straight. Starting with the sales order allows all the activities in the studio to be based on actual demand, not forecasts. It lets you make product only if there is a need for it, so less time and materials are wasted. Pulling materials through your production system keeps everything neat and efficient.
If you instead run your system according to forecasts, pushing on the noodle, you keep piling in raw material and storing it, making product without waiting for actual demand, and storing it even if no one is buying it. You run out of some products because they are more popular than you expected and you haven’t put time to make them in your schedule. You keep making product because of the forecasted schedule, and not because of what your customers are actually buying. Pushing on your production system should be avoided whenever possible.