I’m not sure I understand the point of Amazon Day

…Isn’t the point of Amazon Prime to get your items sooner without having to pay for shipping? So what’s the point of Amazon Day? Now, if it were an option to let me choose which delivery service to use (I’d much prefer having my packages come via USPS rather than UPS, as the postal service carriers can get into my building while UPS cannot), I would be all over this.