In recent builds i would say the most crucial point in order to have successful attacks (and not get every swing PBed or mblocked, or constantly miss and get interrupted), is to make sure that your attacks are started up close to your opponent. You may still get PBed especially if your swinging pattern gets predictable, but it won't be quite as often as if you start attacks from a distance (and in that case it's also easy for the enemy to dodge and interrupt you). Yawing will help getting PBed even less but it's more of a polishing technique than anything, the key point is starting attacks close, the closer the better.
Of course, getting closer also means that the opponent's attacks will also be harder to PB, so it's all about footwork and timing to get your attack to start up close while maintaining more distance when he starts his attacks. Sometimes opponents also won't even let you get closer, they will step back when you walk or run closer in an attempt to confuse your timings; sometimes they will instead attack you immediately as soon as you make it seem like you are coming closer. So you need to be ready for all that in order to keep good footwork and timings. The act of closing in to attack already puts you at a disadvantage because you open yourself to the opponent, he can decide to run away or attack you before you start an attack yourself. So in order to avoid being put at a disadvantage you need to close in subtly and carefully, ready for any reaction from the opponent, ready to immediately back off again if you need to in order not to lose the timing battle; as opposed to closing in straightforwardly and immediately starting an attack.
For that, you need to bait the opponent, for example make it seem like you are going to rush in, then stop and see what the opponent does. Then again. Then, unpredictably, you actually close in and attack. The point being that the opponent must not be able to read/predict what you are going to do. A useful tactic can be to attack from a distance but instead miss on purpose, chain another swing in the air and hit that one; it allows you to close in, bait the enemy to PB and thus mess up his prediction, and then allows you to start an attack (the one chained in the air) from up close thus hard to PB. Of course the opponent may not try to PB and instead run away and try to interrupt you, so you need to be able to react to that appropriately (backing off).
All of this, while meant to be tips for attacking, can obviously be seen from the opposite point of view when the opponent is the one trying to close in and rush you. Anyways in short, yawing does help but it's not a key tactic in order to win duels, if you outskill and outsmart your opponents with better positioning, timing and mind games it won't matter if they yaw and you don't. Except at the top tier of dueling where people already do most things very well so it will be quite hard to fill the small gap in effectiveness introduced by yawing with something else.