It was once the defacto exchange and wallet manager for bitcoin. I believe the statistics were that 90% of all transactions happened on the exchange. In fact,

It was once the defacto exchange and wallet manager for bitcoin. I believe the statistics were that 90% of all transactions happened on the exchange. In fact, once they pulled the server for maintenance, the price of bitcoin plummeted. After it's collapse, a void was created for other exchanges to rise. A more balanced system ensued.