Not sure I understand your question.
On my boat, I have the motor swivel tight enough so that it will not move on its own, but I could move it if I had to. Having said that, it is tyoically set at a slight angle to counter the 'prop walk' and its offset postion on the port side of the transom. (if set set straight, the boat under power would turn slightly to starboard, so the motor points slightly to port aft to counteract this.) Now the boat moves straight ahead under power, and I use the rudder for steerage. The only time I may alter the position of the motor is when I am moving so slow that there is no rudder effect, and I move the motor about to position myself alongside the dock, typically using the 'prop walk' phenomenon to stop the boat's forward momentum as the bow kisses the dock and move the stern to port. During this manouver, the rudder moves unimpeded.