Arguments for looking at the CB last
I look at the OB first to set my aim line.
Once my bridge is planted, I look at the CB.
1. If my aim line was correctly set to start with, I don't need to see the OB last. (It is not moving from where I last saw it!)
2. Monitoring the CB last (or, better said, my CUE TIP) helps to ensure I hit with the
A. chosen English,
C. follow through, and
D. I can monitor my stroke for straightness
In other words, I have better success monitoring and executing a good stroke on the right contact point of the CB than I do by looking at the OB last.
But hey, you do what works for you.