Certification, when provided by a legitimate, recognized institution, is proof that you are an expert in that field or with that particular software and that you possess a particular set of skills. Some employers seek certification to help ensure that the are hiring experts that won't need in-depth or expensive on-the-job training.
In desktop publishing, some designers seek ACE (Adobe Certified Expert) status for Illustrator, Photoshop, InDesign, and other Adobe products. In addition to software certification, some designers may wish to pursue a certification in graphic design or desktop publishing in lieu of a degree program. The skills taught and the value of that certification may vary greatly from one institution to the next.
For more discussion of the value of certification in desktop publishing see:


