You must get a stamp on your PP to get plastic card
It is called I-551 and is a temporary evidence of permanent residence until you get your plastic card. They will not issue you a plastic card if you don\'t go for a PP stamp. Your approval notice for I-485 will have very clear instructions for your passport stamping. Perhaps, your friend is confused about the GC process. Just follow what the INS instructs you each time during your entire GC process.
BTW, I-551 stamp on the passport can be used for both travel and employment purposes. So, you don\'t have to apply for Visa, H-1s, or EADs anymore.