It was not intended to be an alternative to port forwarding and it's very very bad if you use it for that.
It's intended purpose is playing LAN games over the internet.
Port forwarding is very simple and the only reason you should have for not being able to do it is if you don't have permission, or if you're using one of those stuffty bell router/modem combo pieces of stuff.
And if you don't have permission, whoever is in control of said situation is probably too dumb to disable UPnP, assuming your router isn't a dinosaur and supports it.