The Steve Nash partner passing drill is going to work on passing off of the dribble with one hand. This will come into play a lot with point guards, or players that handle the basketball a lot within the offense. The reason that it is important to be able to execute this type of pass off of the dribble is because sometimes there is not enough time for the player to pick the basketball up with both hands, and then make the pass. There may be a cutter that pops open, and there is only a small window to get the ball to them.
By adding the double between the legs move in between each pass, you are simulating a player being in the middle of breaking down their defender, and you are also making it a basketball dribbling drill as well. A big key to the drill is making sure that the players do their best to snap their passes in a straight line to each other. Also, this pass shouldn't be used in a game situation until developed. Otherwise it will most likely end up in a turnover.