Before I ever did Yoko Aruki, I had about 1 year of Aikido experience. In Aikido, we have two movements that are used as one exercise called Irimi Tenkan. I'm sure some have heard of it. Anyway, one steps foreward half step, followed by a full step and a pivot, until facing the opposite direction. This rotation proves to be the unbalance point (for the attacker) in a lot of attacks. when using Yoko Aruki, if caught up in a state of unbalance, it is practical to Tenkan (turn). doing so will not only free you of unbalance, but throw your Uke off as well. It all goes back to rotating the hips, which can be found in almost all MA.