I get such a laugh out of people who are afraid to drive there cars hard. My current 99 GT has a stock T45, a Spec Stage 1 clutch and 4.10's. I drive the car hard especailly at the strip. Id guess I have over 50 passes, powershifted every single time and have yet to have any transmission problems. Not to mention the other 3 5.0 5 speeds Ive had that were treated the same way. If you know what your doing and you stay on top of maintance, your not gonna hurt your trans with a few powershifts.
As for the benefits consider this... My buddy called and asked me to drive his car a few times at the track last weekend. He ran a 13.5 and a 13.9, he let another friend drive and he hit a 13.7. He told me to powershift the hell outta it, my only run....13.21