Trim, bleed and quiet areas
From a sharp cutting blade falling short of a trim size to a shift in how paper is layered up for a print run, sometimes printing machines need allowances in case inaccuracies occur during a print run.
One essential way to avoid issues is submitting your print files to Mixam with bleed. A bleed means your print work extends beyond the trim line to prevent white edges from appearing. If there is a slight cutting variance - you will not get exposed, unprinted edges. Quiet areas will also ensure you keep any vital design elements away from the page edge.
Similarly, colors can move when printing 4-color CMYK ink from metal plates in high-volume litho print runs. To help prevent this, we strategically print lighter colors first, followed by the darker colors, to avoid white lines between two blocks of color appearing if any manufacturing variance occurs.