actualy it is to manuver the stern of the ship better for in the port, like the normal bridge can't see what happens to the back of the ship, but the sternbridge CAN see that, so it is just for making the ship better to move in the port
I doubt that because rudder would have very little effect when navigating near the pier at very slow speed. Center propel would be cut off so there would be little water wash around the rudder. It would also require that the command was transferred to docking bridge. Also they had tugs to make the final navigating.
But you are right that they would have better view from there. My guess it that they would only relay the engine suggestions to the bridge and leave the final manuvering to the tugs. (The telegraphs on the docking bridge was connected to the bridge and not directly to the engine room).
There is this famous film of what was said to be Titanic backing off from a pier. It was actually Olympic. The film shows tugboats assisting in moving the Olympic away from the pier.
But you are indeed right that the wheel could be used to operate the rudder. I am not sure but would there be some form of handle in the engine room somewhere so only the bridge wheel or the aft. docking bridge wheel would work.
If they ever used the wheel on the aft.docking bridge it would have to have happened on eighter the Olympic or the Britannic. I have never seen anything about this, but then again I have never seen that they would not use it, so my knowledge of this is very limited