In the short term, the ions produced by an ionic hair dryer help reduce static electricity. Ordinary blow dryers tend to produce static electricity. Having extra charged particles (ions) in the air allows any built-up electrical charge (static electricity) to be transferred through the air to other nearby surfaces. But this is only a temporary effect. The "frizzy" effects of static electricity fade within a few minutes anyway. Using hair gel or conditioner would have a much stronger and lasting effect than ions, which only exist while the hair dryer is running. In the long term, ions are more reactive than other molecules, so they probably cause the hair and/or natural oils to be oxidized and the hair to become more brittle. But this is probably a smaller effect than the use of conditioners (good) or hot air (bad). Ionic generators also generate ozone, which would be good high in the atmosphere, but it's unhealthy here at ground level. Ground-level ozone contributes to smog and can cause lung irritation.

That is a really interesting question. Ive wondered the same thing about ionic hair dryers.The idea behind ionic hair dryers is that they blow negatively charged ions into your hair. Since hair is made up of positively charged proteins, and opposites attract, the negative ions are supposed to stick to your hair and trap in the moisture. So although ionic hair dryers might not dry your hair any faster than regular hair dryers, they might help stop it from drying out and give it a little more shine.