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Well, I asked that question myself a while ago, and all in all, this is what people said: technically, a slight (very slight) amount of power savings due to the chain turning radius being larger, a slight decrease in wear for the same reason, and... better looks. That's pretty much it. Oh, but a slightly higher weight though. None of this is super important for someone who isn't racing at a relatively decent level, I don't think.
The thing about gearing though is that 59/21 (2.81) or 60/21 (2.86) is almost the same ratio as 48/17 (2.82), but it LOOKS more extreme. ;)
It's offset by a similarly massive cog at the back, but goddammit it looks good. Makes me think about changing my gearing again, I went from 48/17 to 51/18 mostly for the looks - seems like I should go 60/21 instead :D