"Retain Schedule Board operation order" is a scheduler option that instructs the scheduler to retain the order of operations as defined in the Schedule Board.    If you have used the Schedule Board to reorder operations, you can select this option when running a new schedule and the scheduler will try and maintain the same order of operations as defined in the Schedule Board.  Capacity constraints and job flows will cause the scheduler to override the schedule board order of operations.  If you are not using the Schedule Board to reorder operations or you want the scheduler to order operations as required, you can leave this option unchecked.