[irrational]

Also notice how far his shoulders rotate. I see lots of people mainly moving their arms instead of rotating their entire torsos.

[taurath]

Thats been a big thing for me to learn - if you want to be able to breath without taking long pauses, your whole torso needs to move, and it creates a very natural motion to pop your head left or right to breathe a pocket of air

[gideon_b]

Another bonus to rolling -- it is initiated with your core, so it uses large powerful muscles. Once the roll is initiated you can feed your kick and your pull with that momentum. You end up using more powerful muscles to feed your stroke, so you can pull harder without wearing out your arms.