Print on demand (POD) allows producing branded merchandise without an upfront investment.
Using traditional printing methods, such as screen printing, typically requires ordering printed stock in bulk to make it economically viable. This inherently involves some risk on the merchants’ part, as they will have invested their capital in the production of the goods.
POD eliminates this risk since all products are printed only when they've been ordered. This allows you to have merch stores with little to no capital.