One of the main benefits being reported here is the instant purchase, however with Amazon Prime Now (1-2 hour delivery of some items in metropolitan areas), this somewhat goes away. I recently used Amazon to buy new computer parts to upgrade my PC, and when they arrived and I started assembling it, I realized I had gotten the wrong RAM. So even at 9pm I was able to order 2 sticks of decent 8GB ddr4 ram and get it delivered that same night by 10pm and finish the build.
What I prefer about Amazon are the reviews and selection. Even when I'm in Best buy, I'm on my phone reading Amazon reviews for the products I'm considering and exploring alternatives.