For what it's worth, I took both the old MCAT in 2012 and the new MCAT2015 last September and this is what my experience has taught me.
The triaging process was useful in the previous version of the exam, which was such a time crunch. Many students would outright guess on 1 or 2 passages worth of questions because they simply ran out of time. So to maximize your points, you took 60-90 seconds to rank the passages in order of perceived difficulty based on a quick scan of the article and accompanying questions, toss out guesses on the two most difficult passages, and focus your remaining time on the remaining passages. The idea was that as long as you could get a 80-90% hit rate on those passages, anything you got right on the guessed passages was just bonus.
NOW, for MCAT2015, they have reformated the old VR section into the CARS section, which has added time per passage. The general consensus is that all students (excluding those qualifying for accomodations) ought to be capable of successfully tackling all of the passages and questions in the time provided. So taking the time to go through and rank them is actually counterproductive and time-wasting, as you will be getting to all the passages anyways.
