My take on it? Pure and utter bullshit. Just another wrong idea that some genius came up with. The last thing that you want to do is be playing around with the clutch as you approach a turn, especially coming down from a high speed.
In fact, since most cars seem to have greater front brake bias, reving to 6K and downshifting will provide significant engine braking to help with deceleration. Let the slow guys do clutch-in braking.