The weight savings is significant.
Moving the torque points outward is significant.

I've got a set of FSA Team Issue Pro carbon cranks on an Octalink 6500 BB. Great crankset.
I've got a set of FSA BB386 SL-K Light carbon cranks on a BB386 BB. Great crankset.
You can feel the difference when climbing, and the scale says there's a good weight savings.
Otherwise, no biggie, and I don't really notice on my Ironman frames.

Now, on a Felt AR3 I had, you definitely knew when you had an outboard BB.
The difference, however, between the BB386 FSA and a Dura Ace 7800 was neglible all around, and the DA looked better on that particular bike.

At one time, I thought Octalink and Isis were the bomb. Like others, I can't stand PressFit crap, maybe just on principle.
A friend has a CAAD10 and a SuperSix, and even with Campy, it's weird to look down and see the cup spinning with the crank.

Hollowtech II is so easy to install, I think only BB386 is easier.