Not just that - if you can get an entire shopping trip worth of stuff in one trip to a big warehouse-store, toss it all in your trunk, you don't need to fit it all in standardized boxes with bubble-plastic padding, and the distance from warehouse to your house will be covered in the most direct route. Even if you valued your own time at market rates, it would probably take less of your time than it would of someone else's, because shipping has more intermediate steps.