The term "Regular" refers to uniformity. Regular poles consist of verts with each connecting edge being either the same length or very similar. Keeping poles regular means the vert of that pole will move very little or not at all in relation to those edges. If your goal is to get even surface shading distribution, you should aim for regularity. Regular poles are the most common and desirable, but irregular poles are not always bad and have great uses in more complex models.