It's generally considered the best way to defend corners and ironically can be a more attacking tactic. Statistics show that the more players in the box the harder it is to score which is why they like to pack the penalty area when defending corners. It also sucks up the opponents defenders giving more space for a potential breakaway. You would be more likely to leave a player up the pitch if you want him to hold up play if it gets to him. There's very little likelihood of him actually scoring a goal on his own.
Do you have a link to these statistics?
I disagree that it sucks up defenders, because the oppostion will tend to leave the two fullbacks on the half way line regardless of whether we leave any up or not. We should be able to leave one up and still have a man advantage in the box.
Whilst it may be better to pack the box with bodies to deal with the corner itself. I would hazard a guess that these statistics you speak of don't consider the wider consequences of conceding goals from the second phase of a corner when we have cleared the ball, given possession back the opposition and allowed them to come straight back at us. In my mind, that is just asking for trouble.
Its not just about counter-attacking with the aim of scoring either, its about clearing the danger in a way that prevents it coming back straight away. That may just involve the Holding striker holding the ball whilst his team mates re-position following the clearance and give us the chance to build something from that.