I think you understand the difference in meaning. "Walk over to" is a simple action where the subject moves to a location at a walking pace:
I spotted Mary across the crowded room and walked over to her. "Some party, huh?" I asked, with all the casual cool I could summon.
"Walk someone over to" is a different action where you guide someone to some location at a walking pace.
The student looked lost, so I walked him over to the administration building where he could register for classes.
Depending on the context, "walk someone over to" can also imply coercion, or threat of force.
The guards lined up the prisoners and walked them over to the gates of the dentention camp, watching them carefully the entire way.