The most benefit of high index lenses is they are much thinner and lighter than standard lenses. You will feel more comfortable and have clearer view with them But they are much expensive than regular lenses.
Compared to conventional lenses, high index lenses are much thinner and lighter. However, high index lenses are more reflective and expensive than conventional lenses. If you want to get high index lens, you can ask the optician to add an anti-reflective coating to the lenses. If you have a strong prescription, you'd better get high index lens with anti-reflective coating. Though it is expensive, it worths.