Quoted from Pimp77:
A few uses...re-lighting kickback at the captive ball when the ball drops out of the pops, kicking over barrels after the ball leaves the pops to work towards an extra ball, and the mode where you have to hit the Smaug targets following a kickback to the right orbit (and killing Smaug in Smaug multiball). It's useful for hitting the Orc or goblin beasts if running out of time too.
I never understood nor supported all of the negativity regarding the 3rd flipper. But now as an owner, I honestly don't see all that much value in it.
99% of the time, an upper flipper shot is not good for much. Certainly nothing specific that you can't hit with the other flippers.
It doesn't make the game suck, but it sure could've been better if there was a rewarding shot attainable only by the upper flipper (i.e., TSPP Treehouse ramp.)
Perhaps future rules might make it more purposeful, but the current uses offer very few reasons to defend it.