It is the standard Protection filter most people are familiar with. It can help protect your valuable investment from dust, moisture and scratches, which can lead to costly repairs. A Protective filter is probably the most popular filter people use. As a lens protector, it should be left on at all times to guard against front element damage but also adds the benefit of rendering your images clearer.
A Protective filter is also the best available protection against accidental damage to the front element of your lens. A lens that accidentally gets dropped on its front element while hiking can potentially be saved by purchasing this item. Some people refer to it as "cheap insurance".