Die layout looks like a technical detail. It is the single biggest lever on material efficiency, stripping reliability and whether the web survives the run.
The gap is the skeleton of liner left between two die-cut labels. Too narrow and the skeleton tears during stripping, which stops the line. Too wide and you pay for liner and adhesive that ends up as waste. Two millimetres is the working minimum on most rotary dies.
The 3 mm margin along each edge of the web is what the die and the slitter register against. Reduce it and the die starts cutting into the edge, which shows up downstream as a web break at speed rather than as a visible defect.
We slit from 1,070 mm masters, so the number of labels across is a function of your die width plus gaps and margins. A 3 mm change in label width can flip the layout from 4-across to 3-across and change the material cost per thousand by double digits.
If a label has been running for years on a layout designed for a different web width, it is worth re-checking. We quote the layout arithmetic with every order: labels across, gap, margin, and the resulting material yield.
Either a die drawing, or the label dimensions and the direction of unroll. From those we return a proposed layout with the gap and margin stated, so the number in the quote can be checked against the drawing.