^ Not true strictly speaking chaps.
At stock or Stage 1 levels of tune the airbox is fine and does a good job. It's not really restrictive at this point.
At higher levels of tune, there's plenty to be had from an aftermarket intake. At big turbo levels, the stock airbox would certainly be throttling the flow.
Plenty run aftermarket intakes on Stage 1 maps though. They're only really unreliable or detrimental to performance if the maf scaling is wrong, and it helps to have a map that accounts for the intake.