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Apart from the obvious advantages like wet weather braking, the main reason is probably not having to replace rims. I would never buy 💷💷💷 rims that I know will wear out over a year or so, but if there is no brake wear to worry about then why not?
Also, the weight isn't a problem for me, I weigh so little. The aesthetics are no worse than rim brakes and prices will drop ¯_(ツ)_/¯
I don't actually want a CAAD, it just has the same geometry as the Supersix. If Cannondale release a Supersix disc and hydro-eTap is out by then... Then we'll see.