When you run your own store, the parcel is part of the brand. Customers who found you through an ad or a search expect the box at their door to look like the site they bought from, not a plain carton from a marketplace.
The practical challenge is range. You may sell ten SKUs and ship orders of one, two or five items. This page helps you build a small set of sizes that covers most baskets, keep parcels compact for your courier partner, and restock printed packaging in batches that match your sales.