I can get basically anything I want at cheaper prices than locally available by the next day. I can get an increasing amount of things delivered to me same day as well which is pretty nice. The return policy is also a big part of it. There’s basically no fuss or questions asked for anything you want a refund on. You don’t even have to put it in a box, you can just drop it off at the UPS store.
They’re evil, but it’s pretty great from a user perspective.