I kind of know what it is, but I will let one of the experienced power lifters explian it to you better.

If something does not help build muscle, I dont really concern myself with it. Maybe it does though, im just guessing that it does not.

Bench shirt or suit is a tight outfit that enables you to push more weight because it's so tight and thick, but it's main purpose is to prevent injury. With heavy weight, you are prone to injury. This will prevent major shoulder damage, pec tears, etc.

I think that sums it up, but I'm not too familiar with suits.

Also, they're expensive, and look cool

Just do a search bro. It's a piece of equiptment now used in competition to prevent injury and allow you to lift more than you really can. It's not cheating thought because everyone can use them. I just think it's ridiculous that say Scott Mendelson couldn't make like 1000 and change touch his chest which means that at the bottom that shirt alone was holding more than 1000 lbs.

a bench shirt is made of a special denim. it's really tight and elasticy (i made up that word lol). as the other guys pointed out it can enable you to move greater loads and prevent injury (especially to the delts and RCs) too. mendelson has a 1008 lb shirted bench press which is the world record (held jointly with gene rychlak) but he also has the raw record (unshirted) of 725lbs but by and last, raw benching and shirted benching are 2 different animals because of the difference in grips required. typically shirted benching requires a much wider grip and bringing the bar down lower on the torso.

I don't have time to respond to this right now but I will get to it. In the mean time PB? Dadawg?