Better holding of boost, greater power potential as more gasses can escape quickly through the larger hole etc. etc.

You have to spend alot on a decent external actuator though as the stems can bend due to the high amounts of heat. Once bent they will not seat properly which will increase your lag as the turbo will not spin up as fast due to the leak.

Stick to normal type actuator unless you want to spend £15k+ on a 600bhp+ motor