Magic Knot or Double Knot

In the Knit4Charities Group that I belong to Pam, who is the founder of the group, shared a link for a youtube video on how to create a magic knot when joining your yarn. I personally haven't tried it yet but that's only because I am using small bits of yarn that doesn't need to be joined. I found it interesting and I know I will be trying it sooner or later. I'm not sure how it will got for crochet work and lots of colour changes but I guess if you are using one colour it would be good.