I've been told that if you use the 2-man method for bleeding brakes (one man at the bleed valve with a PVC tube over the nipple, one pumping pedal) you can damage the seals as "the brake shaft goes further than it's intended". They went on to say you should never press the brake pedal all the way down to the floor when the bleed valve is open on one of the calipers using this method.
I don't know what they mean but has anyone heard this? They advise only ever use the vacuum method. Weird cos half of youtube is bleeding with 2 man method:/