Bleed is extra art that extends beyond your finished size.
Bleeds must extend at least 0.125 inches past the intended cut line to allow for slight misregistration in cutting or finishing. If we are producing a large item like a banner the image or color must extend 1 inch past the finished edge. In the case that bleed is not provided, while there are workarounds available, your final product may not look exactly as intended.
The purpose of bleed is tied into how we actually produce printed items, especially if the finished item has artwork all the way to the edge. When we print a product, we can’t actually print all the way to the edge of the paper, just based on how the machines work.
Our production process lays out the printed piece on a sheet larger than the final product. If we can, we try to include multiple pieces per sheet, printing them 2-up so we can use less paper and print more quickly.
After things have been printed, the items are cut to final size (for flat items) or folded and assembled and then trimmed to the final size (for booklets or other multi-page products).