I think the most relevant answer on the thread so far was Chris's post about how it relates to entering and working around your opponents limbs.
The start point is pretty key as well I think. Both people in the "peng position". It's the moment of change. Like a Ouiji board. There is no rule as to who transitions to an and who to ji but I was just thinking more simply that that is essentially an "on guard" stance. One hand high and one hand low.
The little switch off between the hand and the elbow that you have to do to avoid getting your arms crossed is pretty tricky too. I've not met anyone yet without at least 3 or 4 years of push hands training who could pull it off without getting pushed if I just gave them a little real "an" at that point instead of moving mechanically through the routine. It's like a little hidden single palm change but where instead of hiding the flower under the leaf, you hide the leaf under the lotus.
The way the hands contact is a lesson from that pattern too. You can't place your palms on the other guy at any point or you can be locked. Actually, back of hand is the same. You have to use the blade.
That particular pattern also presents entry points to practice numerous applications and their counters. It encourages that application of the tactical arsenal contained within the taiji form.