If you crochet or knit you know that when you have to add a new color or a new skein of yarn you have to know the ends and then weave the cut ends into your work.
While this method works there are many time that after washing the ends work themselves back out and you have to sit and reweave them back in again.
This Russian join method shown by Twisty yarn shop eliminated the loose ends. You actually work the yarn ends together and they leave no long ends to be worked into the piece.
Very nice tip.