I can attest to the reasoning behind this. Many people love collecting pressed pennies. The traditional systems always have one flaw...what people put into them. The "wrong" pennies can damage and take it out of circulation until fixed. Never failed that a machine I needed was down. By controlling the media that is used to make the press is consistent, the machine will be active much longer.
I started this adventure using only 1972 pennies. It got expensive finding them because there was a mis-strike on the year which made values very high if found. I did the same with 1971 quarters. I still have a collection of them to use, but have over 500 pressed in this method.