Staples cause their own problems for postal equipment. Mailing pieces can no longer be stapled closed if you opt to receive automation compatible rates.

Even saddle stitching or staples in the spine of a mailing piece can disqualify a mailer for automation compatible rates. The ends of staples can not be protruding and if possible should be imbedded in the surface of the paper. The alternative to imbedding is gluing the pages together. This requires design considerations since coated stocks and printed areas may be compromised by gluing.