The purpose of the shirt is simply to be able to lift more weight. The excuse that it is to protect from injuries is just a canned respose that most "not all" powerlifters give when question about the shirts. If anything injures have increased from the shirts due to people trying much more weight that theyre body can handle. I have seen many times where a lifter in a shirt gets "out of the grove" and the bar goes flying towards their head. If a shirt blows out, its very ugly. If anyone can show me satistics that shows a decline in injuries since shirts got very popular, I'd love to take a look at it.
I have only seen a handful of powerlifters be honest and say the only purpose for the shirt is so they can lift more weight which I can respect I mean, they're often very strong guys but no matter how strong you are the shirt is BS IMO. Just don't fall for the canned "it's to protect my shoulders line." Sure you going to injure yourself if you try raw a weight that your body cannot come close to handling.
Why do you think powerlifters with shirts do a TON of board presses? The purpose of that is to strengthen the lockout part of the lift. Why do they focus on that so much? Well its because the shirt does most of the work through the bottom part of the lift and the assistance fades as it gets closer and closer to lockout.
Real life senario. I was at a powerlifting meet. Competetor has on a Titan Fury Bench press shirt which feels like a shirt made out of seat belt material. After powdering him up and taking 3 guys to get the thing on him, he walks up like a undead zombie arms extended to try to live 550lbs. He brings the bar down, but CAN'T get it to touch his chest "about 3-4 inches away" easily does the lift but it doesn't count because he didn't touch his chest. He then UP'S the weight to 600lbs and again, next lift he can't touch his chest. Then the weight for his final attempt gets raised to 620 and yet again, he's about an inch away this time. He bombed out because his shirt was so tight that he couldn't make over 600lbs touch his chest. Even the referee "an old school lifter was shaking his head."