What is Hair analysis used for?

Personally, I am utterly skeptical. I have researched and pondered this issue, but considering how slowly hair grows, I cannot fathom how a snip of hair taken from even as little 3 inches from the scalp can provide relevant information regarding that person's health and nutritional needs. The local wholistic health providers here claim it is accepted by many people all over the world, but I have yet to see any convincing data supporting this claim.