If someone aims with a focus on the contact point, it is clearly helpful to look at that point. As someone who doesn't look at a specific point on the OB, I have another reason for OB last:
My method is to look at the OB (not a specific point, just as a whole) while being aware of the CB and cue in my peripheral vision, and focus on the mental image of 1. the cue going perfectly straight, and 2. the shot image staying completely still (or in other words, not moving anything except the shooting arm). If these two things happen, the shot will go in, assuming I was properly aligned with the cue, which I pay great attention to before shooting.
With this approach, the reason for looking at the OB last being better is that, looking at the CB means the OB is blurry in my peripheral vision, but looking at the OB still keeps the CB and cue clear in my peripheral vision. And it is clear that a non-blurry image is more effective for the subconsciousness to work with in terms of shooting straight and staying still.
So OB last simply provides a clearer visual image of everything relevant compared to CB last, and that is why I do it.
Obviously none of this matters for the easy shots, but you should always build your technique around the shots where you start missing due to imperfections.