Now, I am not an extremely advanced piano player, but I do have my fair share of experience in other fields of music as well, so here is my opinion.
The metronome is an invaluable tool for making sure you aren't being lazy with your time. I've played with several classical musicians* who wanted to put on a more contemporary/modern/poppy/jazzy kind of concert, and they have been absolute hell to play with because of their inability to maintain a consistent pulse.
The main reason I feel that others find no benefit from using a metronome is because they're using it in the wrong way! In order to use it to it's maximum potential, you have to do what a few others have said here, and keep it from clicking on every single beat. Perhaps let it only click on the 2 and the 4, or maybe the 2 of a 3/4 pattern.
As soon as you've mastered a piece with a metronome, you should get off of it, JUST FOR THAT PIECE. Take what liberties you need with the piece, or not. Once you've really learned a tune like that, you don't have to worry about what you're able to, or not able to do, and you can just focus on what you want to hear.
All in my opinion, of course!
*I say classical musicians here because I find that there is much more of a tendency to dismiss the metronome in a classical setting rather than a jazz or more pop oriented style.