The advantages about 4C? It's a preempt, and preempts work. Since we are vul, partner would expect me to have my bid, thus he can judge the situation (raising to game, penalising them etc). Plus, people rarely X 4m openings for penalties and they have a hard time to judge whether it's safe to come into the auction or not as opposed to opening it 5C, which they can easily hit that. Don't you just love it when it goes 4C - (4M) - X.