Q: Why is bleed important?

A: In commercial 4 color printing, all final jobs are cut in stacks. The accuracy of cutting in stacks is never perfect. If bleed is not provided on a document, the final result of a trimmed job may possibly result in a slight white border around the edge.

The example below illustrates why bleed is important:

In this example the business card had no bleed so the final cut left a white border.