So why should I care?
Well, first of all (and mainly), it can and will save you money on individual purchases. You can find pretty much anything you want, and chances are, the prices will be the lowest up front -- especially compared to traditional grocery stores, and even compared to Amazon.
For example, this 35-pack of Diet Coke is $24.40 on Amazon (again, already cheaper than most brick-and-mortar stores). On Jet, it's $12.11. If you flunked first grade, that's a $12 difference, and that's just the tip of the e-commerce culinary iceberg.
That, and it means you don't have to lug groceries to your front door -- or 12-packs of LaCroix up to your eighth-floor walk-up. That's a plus.