Exploring the distribution channel at Amazon

Based in Seattle, Washington, Amazon began as an online bookseller, although it now has branched out into software, video games, electronics, apparel, furniture, food, and toys. Founded in 1994, Amazons business plan was unique in that it sold only through the Internet. Customer orders were filled by using books purchased from channel distributors. This strategy was considered radical at the time, and it contrasted with traditional brick-and-mortar stores which usually purchased directly from publishers and then inventoried in expectation of customer sales. To facilitate sales, Amazon began to open its own fulfillment centers. As of 2012, Amazon had 22 fulfillment centers across the United States and another 15 in the rest of the world. Today, Amazon stocks a wide variety of titles, though it still gets many titles directly from distributors and publishers. It uses the United States Postal Service and other package carriers such as UPS and FedEx to send books to its customers.

Questions: Why is Amazon establishing more fulfillment centers as it grows? What is the negative side of this strategy?