In the case of my AEM PEMS stand-alone, I have full and complete control over the boost control solenoids operation - the result? I can make my VF30 spool faster and quicker - then hold boost better than the little stock turbo and boost control configuration.
The stock configuration is basically a bleed system - it controls how much boost pressure is bled away from the wastegate. The problem is - the wastegate is always connected to the turbo compressor. By switching to the GM solenoid (or similar), you can keep the wastegate closed completely while you are spooling up - then pop it open just in time to prevent overboosting. It's quite impressive.
The drawback - you do require something that will let you control the new solenoid - I can't tell you what those options are - just that it's well worth it in terms of how the car responds.