Home printing leaves a plain 2mm gap between cards, sized to stay inside a typical printer's hardware margin. Printshop instead extends each card 1.5mm past its edge with a solid black bleed, so the two neighboring cards' edges meet with no blank paper between them — an imprecise trim lands on black rather than a white sliver, matching the cards' dark borders.
Example output page (click to enlarge) — cards are printed at full size with a small gap between them, so cutting doesn't slice into a neighboring card.