You probably won’t see much difference for AI-controlled characters, but for your player character the difference is this:
“Orient Rotation to Movement”: Your character will turn to face the direction of travel. No matter which way the camera is facing, your character will always face the direction in which he or she is moving.
“Use Controller Desired Rotation”: Your character will orient to the direction of the controller rotation. In most games, this is visually represented by the direction of the camera so your character’s back is always to the camera and he or she rotates to match when the camera is swung. Of course, you can decouple your camera from following the control rotation as well so a more accurate description is that the character will face whichever direction the “right stick” or “Mouse X” is pointing.
Again, you don’t control the AI so both of these options look identical to a third party. I think “Orient Rotation to Movement” looks more natural, but there’s really no big difference, visual or otherwise, for the AI.