If you lean in to a corner with or more than the bike and the tyres slide out you will hit the deck as the force holding you up relies on the friction force between your tyre and the floor.
If you position your weight over the contact patch then even if or when the bike slides you will not fall over and you will soon find drifting the bike much more controllable. This in-turn allows you to ride closer to the limit. This method of cornering also increased the force acting directly downward into the contact patch of your tyre which increases the friction. Allowing you to go faster without sliding.
This is how I understood it anyway. As soon as I started leaning the bike over and opening my body to the exit of the corner I instantly felt more comfortable and more in control of the bike.