Hi,
UPnP is a set of protocols developed to try and bring the same degree of simplicity (*cough*) to the installation of network devices as has been done to PCI like devices.
I guess that unless you have UPnP enabled network devices and you're using UPnP aware drivers to help configure them, then you can safely turn this feature off.
BTW I would suggest that this post is better placed in the GH/Network/TS forums? It isn't highly technical and probably won't draw much traffic here.
Good luck,
Andy