So I've been looking at a lot of warcraft logs for good prot warriors on heroic 10man at the moment I noticed something I should have picked up on myself.
But for a lot of bosses depending on your avoidance it actually seems to be better damage reduction wise to just shield barrier the entire fight.
lets say a boss melee swings for 150k every 2 seconds, 30% = 45k, 45k*3 shield block reduces damage by 135k (assuming you dont parry or dodge)
Shield barrier as a lower estimate on average will be worth about 150k but can go upto 200k and will reduce the full amount of damage unless ofc you avoid 3 consecutive hits, shield block however for every dodge/parry will lose 45k value.
Obviously this is very very simplified doesnt take into account glyph of HR or crit blocking I'd like to hear more opinions though.
Just to illustrate my point heres the log that really really confused about when to shield block and when to shield barrier.
http://www.warcraftlogs.com/reports/...aken&source=11