It is quite common for people to have lower front teeth that are crooked, worn, chipped, etc. Usually it has to do with relapse after braces as a kid. At this point as an adult, even if you had them straightened, they still would be chipped and broken.
By using porcelain veneers, we can give the illusion of having had braces again so the teeth look perfectly straight. The added benefit though is now they also look pretty, like they used to when you were younger. Notice how these teeth look so realistic with color transition, translucency, etc.