Best practise question

programming flash
1

I see in a lot of tutorials that people choose to not give their variables any value inside the class tags, but let the constructor function handle this instead, like this example:

package 
{
    import flash.display.MovieClip;

    public class Example extends MovieClip
    {
        private var myNumber:Number;
        private var myBoolean:Boolean;

        public function Example()
        {
            myNumber = 10;
            myBoolean = true;
        }
    }
}

I’m curious why they do this, is it some sort of best practise thing?