While I do agree with learning as the fight goes in during progression but when others have already done the work and progressed through and defeated the encounter and uploaded their kill to a common video site such as youtube, it's great to be able to analyse the video from the PoV of the role you'll be doing so you can cut out a lot of that guess work and be on the ball and take even less time to get that kill as others have before you.
It's not hard to watch a video to get the general gist of the fight, but the bulk of perfecting the encounter is by doing it and messing up extremely badly causing a wipe therefore burning it into your memory of what not to do.
