uPNP is required if you want your devices to be able to open ports on your router, otherwise you will need to manually do port forwarding. Manual port fowarding gets annoying if you have more than one machine that need that same port at different times, like when my wife wants to patch World of Wacraft or I want to patch it. It uses BitTorrent and requires forwarded ports.
Without uPNP, I would have to sit through slow patch downloads or manually change which computer has that port forwarded.
In the grand scheme of things, it's a security hole and public IP addresses with a proper firewall settings is best.