The size of the waist is an indication of overall fitness for many people. Most health experts agree that a smaller waist is healthier than a big one. The reasoning behind this is that increases in fat around the waist usually result in increased health risks such as diabetes, high cholesterol and blood pressure.
In evolutionary and biological terms, a small waist signifies youth and vitality. But doing endless workouts of crunches alone will not allow you to achieve that Venus-like waist of your dreams. You will need to supplement specific waist-orientated exercises with ones from various disciplines.
Specifically you will need to work the inner girdle of muscles - commonly known as the core muscles - with slow abdominal exercises that work very deep into these muscle groups.
While usually associated with building flexibility, some specific exercises from yoga-based workouts also target the underlying core muscles around the waist.