I think it used to be a trick to fool people that didnt know what they were way back when, then it got discovered. Gigs up. Then they made a sport out of it.
Equipment was originally for injury prevention. Lifters discovered it helped aid in the attempt at greater loads. Then ... Folks did what folks always do: they took it further and further. Now it has gotten insane and utterly stupid.
That so many on a bodybuilding board aren't fully aware of what's going on with equipment in powerlifting tells you how in the dark the average person is. YouTube features gassed lifters wearing multi-ply gear benching over 700 and you get someone here on GetBig saying a 405 press today isn't shit (!).
People, the biggest raw bench is 715 (Scot Mendelson) and NO ONE else is close to this mark, even a few years after the record was performed. Ryan Kennelly, Scot's closest rival, is now in jail, so ...
Generally, the very greatest juiced benchers are pushing between 550 and 650, raw. The multi-ply shirts give, if one regularly uses one and comes to understand how to best derive its max benefit, well over 300 pounds extra weight. Mendelson has posted almost 1100 using one. Again, do the math. Even the single poly shirts today give a lifter about 100 pounds.