Bestseller lists: Are they important?

Oprah’s, The New York Times Bestsellers, Calcott, Calvert’s, Newberry, and every bookstore in the US have them, along with every library system. You can find them for picture books, religious groups and nearly every sub group out there. But are they really necessary? Why do we have bestseller lists? They are intended to showcase certain ideals or stories, but most people, I have discovered, tend to use them as a way to avoid certain books. All they do is show what has sold more, but was that due to reader enjoyment or publicity?

What are your ideas?