The main benefits of wide bars is that they put your weight further forwards. This puts more weight through the front wheel and improves traction, and gives you a more aggressive stance. Of course you can run a longer stem to put your weight forwards but that makes the steering more sluggish. Potentially a wider bar gives you more leverage and makes it less likely that front wheel rocks will force you off line, but my opinion is that's a secondary benefit.
Superstar have obviously taken it too far though - I imagine they offer that to allow people to cut them down to a more reasonable size, but I bet a lot of people won't...
750mm for me on the XC bike.
My view is that wide bars = better, but the last time I said that on here I got mocked by some luddites so I'll end this post with "IMHO, of course."