the point is true, when the engine is cold due to the nature of combustion, an engine, piston/rotary, runs richer. problem is rotaries run already too rich. the idea is taking the rpms up turning the key off and holding the throttle, is to allow leftover fuel to deplete out the back. preventing flooding, and allowing easier startup. rx8 and non peripheral ports should do this more then us b/c of the exhaust design. If you've been driving around, there's isn't a "need" but you can still do it if it makes you feel better
that's the only real purpose it servers especially for rotaries. piston dont' need it b/c all excess fuel will eventually seep past the rings and clear itself anyway... vs a rotary will not. stays at the bottom of the "keg" so to speak.
secondly. 98% of all engine oil pumps are mechanically run. SO, if you let the turbo cool, doing this rev up to clear the fuel will NOT startve the turbo of oil. as long as the engine is spinning, oil is being mechanically fed to the turbo, engine, crank, rotors, etc etc etc. so don't worry about oil starvation. and a good turbo anyway even under idling conditions spins quite a bit longer then the motor on shutdown anyway. if anything.. you can think of it. as your last attempt to get excess fuel, hotter oil and water, for something a bit "fresher" during shut down. regardless it'll all drain back to the pan anyway. so worry not.
my recc... go ahead adn do it if you feel more comfortable. if you don't, then dont' do it. but if you flood on cold start. i charge an hour labor to deflood at the dealer