It keeps your scalp in an optimal condition to grow hair by reducing irritation, and thus MAYBE helps prevent male pattern baldness.
From the website:
Nizoral is a necessary part of any hair loss treatment regimen. On it's own, it will not do much, but it has been proven in clinical studies to increase hair count, and comes as a shampoo which can conveniently be rotated with other shampoo's at a very low cost.