Ever since I was little, I've had calcium deposits on my teeth that appear as little tan spots. The spots aren't that noticeable if you don't already know they are there, but it would be nice not to have them. A few years ago at the dentist, I was advised to try the Crest Whitening Strips to rid myself of the calcium deposits, so I went to the store and shelled out $30 for a box of whitening strips. They felt really weird at first; the gel would kind of seep out and it tasted nasty, the strips were such that I couldn't talk too well without risking dislodging them and tasting more of the icky gel.
Despite my discomfort, they worked and they worked fast. It didn't stay so pleasing though. After three or four days, my teeth started becoming really sensitive and instead of using the whitening strips twice a day as recommended, I had to cut back to once a day, then to once every other day. I couldn't keep going with the twice-a-day plan, but I was also prolonging the pain by not using them everyday. Even with my mitigating efforts, my teeth still proceeded to become more and more sensitive to both hot and cold and eventually even a breeze of air would produce a chronic ache. I was miserable. To this day I've never made it through a whole box even though I've tried again.
Whitening your teeth these days is so easy and pretty affordable. People's teeth are becoming whiter and whiter all the time (sometimes even to the point of a translucent-like blue). Besides Crest there are other brands and even generic brands from Target and Wal-Mart. You can even do it without strips if you'd like; there's a hardening gel for nighttime and trays as opposed to the sometimes-flimsy gel-coated strips.
The question is not whether they work (because they really do make your teeth whiter) but whether they are worth it. I've talked to others who tried the whitening strips and their experience wasn't as painful as mine, so there are people on whom the gel doesn't cause chronic pain, but also most of these people admitted to a little bit of sensitivity. While the strips did warn of increased sensitivity, I had no idea of the pain I would endure until I tried it myself.
The decision of whether or not to whiten your teeth comes entirely down to you. There's no special requirement or appointment you have to make; you just have to decide how far you're willing to go with the strips. Apart from the pain, I like the whitening strips because they produce quick results that last for a while.