The "policy" is inconsistently applied. I book 1F and many times 1D (or it may be 1E) is empty and then other times there is someone sitting there. I asked the pilot (since he was standing next to me) the first time there was someone in the seat next to me and he said if United could sell the seat they would.
My thought was that for a policy that I thought was meant to provide protection for employees it was a sad day that a corporation was willing to make money vs the safety of their employees and then my next thought was well it probably does not really protect the employees.
I continue to book 1F and sometimes there is someone next to me and at other times there is no one next to me. My most recent seatmate had been upgraded into the seat next to me and I am wondering if status may determine the upgrade for the seat? Pure speculation on my part.