when your just putzing around town, the power shift button delays shifts. this makes the car "feel" faster (but wastes gas). at wot, it will still shift at the same time with it on/off, which on my 3.71 geared one, around 6000 when im flooring it, if im only almost flooring it, 5500. 99% of the aurora owners will say the performance shift does nothing, a few will say it feels like there sharper shifts. either way, it for sure doesn't hurt performance, so i use it on the occasional race.
if you drive e everywere with it on your mpg will go down.
i wouldnt worry about babying it TOO much, the 4t80e is a beast. its rated for 305 tq at 6500 rpm shifts, more than it will ever see. even modded your at about 285-290 TQ (intake, exhaust, highflow cat) at 6k shifts, below what a STOCK STS will show it for abuse. come on, the 4.0 loves to be wound up!