Generally speaking, new male drivers will go too fast in a corner or steer too much, or try to brake too far into the corner. Basically, they over drive. For them learning slow in fast out is beneficial because it helps in these three areas.
Generally, new female drivers will take more of an average speed through the whole course. Not going full throttle in the straights and going too fast in the corners. Again, learning Slow In, Fast Out helps with this as well.
In these instances the driver is trying to do mare with the tires than they are capable of. It's called a "Friction Circle". Tires have a maximum grip in every direction. Once exceeded the grip goes down dramatically, so don't try to color outside the line of your Friction Circle.
The first technique to learn is to brake in a straight line, then decrease braking and increase steering in equal amounts (as if your brake and steering wheel are connected by a cable). Then, coming out of the corner, increasing gas and straightening out the steering wheel in equal amounts. This is the easiest way to fill in most of the friction circle. Actually, the pattern is more of a diamond than a circle, but it's getting there.
So I've been hearing a new term, "fast in, faster out". This becomes more of an advanced technique. And it becomes a result when you try to fill in the outer quadrants of the friction circle. These are the steps: First, you threshold brake, then trail brake into the corner (filling in the upper part of the circle), then smoothly transition to full cornering, while applying a small amount of throttle. Then increasing throttle as early as possible without spinning the drive wheels and unwinding the steering wheel.
The tricky part is the the transitions from all of one direction to all of the next direction is not linear. For example, when transitioning from full cornering to full acceleration you will initially be putting in more throttle than the steering that you are taking out. That's how to fill in your Friction Circle. It's something you have to get a feel for. It comes with practice and is one of those things you can concentrate on if you have memorized the course.