i personally think it matters. an old timer at my gym marked a certain brand of 45 pound plates and they all are within .5 lbs of 45. other ones vary. its why for deadlifts ive been using 100 pound plates. the 100 pound plates at my gym are marked exactly what they weigh. 2 of them are more than 1 pound over 100 and the other 2 are less then .75 pounds under 100. same brand, same plate. so, the other day when i deadlifted with them it was actually probably closer to 582-583 pounds and not 580. id prefer to train with heavier weights. or preferably calibrated plates. they do make a difference.