Simple Answer.......................Never

I have two carbon bikes, one w/compact Campy Record, one standard Dura-Ace.

The Compact crank has too many advantages to list.

The smaller ring creates the opportunity for major climbing without a 3rd ring.
The 50T ring allows for closer together ratios, from gear to gear. Great for finding the perfect cadence.

The only disadvantage is spinning out of your top gear while running downhill. You don't spend the majority of your riding time going downhill. I live in the foothills of North Georgia, and there is very little flat ground.

The major crazies are so worried about running in big gears, doing everything the same. 80% of your gear ratios are available on both chainrings. You might be a couple cogs apart in the rear, but they can be amazingly close. Look at Sheldon Brown's charts. You can probably run up to 20-25 mph in a 50-11. You can jump into the big ring for flats and downhills. I ride in the big ring most of the time, but when climbing long and strong, it's great to have the bottom end to work with. In the Tour de Georia, several pros ran triples or compact cranks on the climbing days.

Unless you're a flatlander, I can't see much use for chasing bigger gears, unless you're racing. I have seen 49 mph on both my bikes. Don't need overdrive.