I kinda hate bringing threads back from the dead, but I would like to provide a more reasoned answer to Hugh's post...
If you are on the road not shifting out of gear and are in boost, slow down for a situation an then speed up, recirculating the bow-off will have the turbocharger providing air faster. If you are accelerating through the gears at anything less than maximum boost, recirculating will provide a bit more kick during an upshift.
I see no disadvantage to either - only positives.
Without recirculation provides only negatives.
As far as open a bit during idle, manufacturers use this to provide more air immediately upon throttle tip-in for better response.
Just sayin'...