The locking of the courses "in the same place" prevents the displacement of the courses locked by EDT during an automatic placement. It also prevents the removal of courses by inadvertence during a manual modification: to delete a locked course, you must first unlock it. The manual modifications of a locked course (displacement, de-positioning) depend on what the user has chosen in his/her preferences.
Note: no matter what options are ticked, you can always unlock the course to modify it later.