Originally posted by 89TwinTurboSupra
yes it does, if you have no blow off valve you experience compression surge, which will not alllow you to run any decent amount of boost, and which will damabge your turbo. Therefore it does help your performance.
Upgrading from a stock BOV also increases your performance, because stock BOV's will tend to leak at a certain amount of boost, by replacing it with a stronger one, you can increase your boost, which makes you faster, which is a PERFORMANCE GAIN. 
Any BOV can leak but what you are failing to understand is that there is a difference between a blow off valve and a bypass valve.
They make electronics to compensate for running rich between shifts, one of them being EIDS by HKS on the Super AFR.
Additionally, an Electronic Idle Stabilizer function (EIDS) function, which buffers the dramatic airflow meter signal fluctuations, prevents the engine stalling or stumbling effect associated with the sudden imbalances in the air/fuel ratio of airflow meter-equipped vehicles that utilize discharge blow-off valves that vent to the atmosphere.
I think the SAFC2 also have a function for that aswell.