Well they're stiff so they transmit muscle energy more efficiently to the drive train.
They're lighter in weight for components of the same dimensions, so maybe 10secs faster over 40KM
They dampen vibration somewhat, so, ceteris parabis, you get a silkier ride.
They look cool at the coffee shop and people will talk to you.
They are really expensive so if you're a pro, they make a good tax write-off.
Girls will give you their phone number.

OK, I was kidding about the last one.

Will they enable you to go faster? Maybe.
Are they worth the money? For 10 secs over 40K? Maybe if you're a pro, or Bill Gates.

PoC
The one who dies with the best toys wins.