Durz...
I had a chat with abbey about this as why should I.
Evryone has commented right so far and I think the main reason is for holding the boost corectly and making sure the flow is right.
As the std pipes are rubber they have been known to collapse as higher boost levels, so as your have the steel turbos and may think of running over 1.2 bar then a wise investment, especially as you move to 1.4 bar and over.
Hope this helps.
Plus they look nice!! (if you are a tart like Paul)