Only one copy of the book DOES slow things down, fair enough.
This! The most amazing, virtually unplayable RPG I know.Wraith: The Oblivion - My favorite horror RPG, but very emotionally draining when played "right."
My limiting factor isn't what the rest of my group will play. They'll play virtually anything I'm interested in running.
So, the limiting factor in what I play is... that I don't get to play, because games don't happen unless I run them.