To keep the back straight, or not. Both ways are
shown on WBB examples. What difference does it
make to your workout? How would it hit the back
differently? Or does it?
I am currently using this as my basic back
exercize, alternating with pull ups (I also do
deads on my leg day).
I noticed that I tend to lean backwards instead of being fully perpendicular to the cable. I think it doesn't hurt too much if you keep it in control, but I think that if you end up leaning too far back, you start to include traps posterior delts.
What is probably worse is if you are changing your angle during your movement.