here is a little peice i found just for you. from the website 'turbocharger basics'
pm me if u want the wesite address


"Without the wastegate working properly and allowing enough gas to bypass the exhaust turbine, a phenomenon called "overboosting" occurs where the boost level can run dangerously high. Sometimes fitting a very large bore high flow exhaust can cause this with the stock wastegate."

so imagine what would happen without it