First of all, I circled Pique and Mascherano here to show how far the two center backs are from each other. Why is this important? When Mascherano came to Barcelona in 10/11 season from Liverpool, he told that the best way to help your teammates was to go towards them, to be close to them. In Barcelona they told him to do exactly the opposite of it - to get away from them to always open up a line of path. This is why Barcelona play rondo every day and do exercises with the ball every training, to be comfortable with the ball even in tight situations, so you can positioning your players that far away from your teammates so with couple of passes/movements you can play the ball to the other side of the pitch and to get away from the pressure.
7 Seconds after you can see that the Mascherano have the ball here and they got away from under Valencia's pressure and can build up the attack now, with the pitch spread and players have more freedom because of the made the pitch 'big'.
This sequence here with Iniesta shows how important is to move. Because if you move you drag away defenders. It gives Xavi, with the ball, more options. Iniesta created a path of line for Xavi to play the ball to Messi there. If you look at the 2nd and 3rd picture you can see the difference.
This sequence is only about Xavi's pass to Messi. It's just one pass but there's so much to see here
Lets start with Xavi.
Full sequence of this attack