This move will definitely expand the Apple Watch retail availability leading to more sales. From August 7, you can buy Apple Watch in selected 100 stores but in coming months availability is planned for 300 Best Buy stores in United States.
Apple's spoke-person during an interview with iMore said -
Starting Aug. 7, Best Buy will be the first national retailer, other than Apple Stores, where customers can buy the Apple Watch. It will begin to arrive in more than 100 Best Buy stores and will also be available on BestBuy.com. Another 200 of our stores will have the Apple Watch in time for holiday shopping.
“The Apple Watch is an important addition to an emerging product category, and we know our customers want it,” said Jason Bonfig, senior category officer at Best Buy. “We are excited to bring Apple Watch to more consumers, especially with the holidays coming up.”