Advances in desktop and professional 3D printers have made production faster, more reliable, and significantly cheaper. At the same time, customers increasingly expect personalized products, and businesses want to cut inventory costs. Together, that makes on-demand manufacturing practical for thousands of products that used to be too expensive or risky to produce.
In short
3D printing on demand produces physical products only after they are sold, or in small batches, so designers, businesses, and manufacturers can drop large inventories, reduce risk, and make products only when they are needed.