[zdw]

Certifications are proof that you passed a test. This either means that you memorized a battery of questions, or you actually know the material.

Going with the latter (as the former would be weeded out nearly immediately on the job), it means that you know at least something about a topic, and are able to be trained on it.

Certs are more useful/common in the ops word. Personally I do the training/certification when I want to learn how to run a new operating system or application. It's a motivational time limit, and should teach you the basics at a minimum.

The other reason they're popular is they're a way to jump up the ladder at various workplaces that don't allow other methods of internal advancement, which is pretty dumb.