Very useful when climbing overhangs. You've probably noticed the different shapes of climbing shoes. One style is flat like a regular shoe. The other is pre-shaped in an arch. Shoes are designed around a last, which gives a shoe its basic shape.
Manufacturers have their own unique lasts.
There are 2 categories for climbing shoes, traditional last and a cambered last. The traditional last shape is flat, and the cambered last is arched. The pre-shaped shoe is an advantage, but for longer routes the discomfort makes them impractical. As a beginner you should consider an all-purpose shoe with a traditional last, which allows for all type of surfaces. This shoe isn't of lessor quality and is what most will use on long routes with varying terrain.