I think teeth whitening is a bit like steroids or liposuction. It is mostly for people who have insecurities and/or lack discipline to get quick, visible results at the expense of their health. I'm adding health here because these procedures, although deemed safe, are certainly harmful in some way.

There is a natural yellowing from coffee, tea, smoking and aging that even disciplined hygeine doesn't combat. Whitening (via oxidation) is nothing like surgery, being a meager, inexpensive, 5x5 minute habit that has a pretty big impact on perceived health and grooming. The downside is some temporary damage to your enamel, but it's less than a single cleaning at the dentist. If anything, I'm wary of whitening toothpastes, which are ubiquitous and tend to work via abrasion.