Various authors propose the use of flow dominance in complexity ratings to evaluate the complexity of facilities layout problems, to determine the choice between computer algorithms and visual based methods for plant layout, and to decide on the particular layout configuration (line or process layout) to be installed. This paper examines critically past contributions and casts some serious doubts on the validity of the flow dominance concept and the related measures of layout complexity. It is shown that flow dominance does not serve its intended purpose and that the complexity rating factors suggested in the literature not only show serious problems with regard to their interpretability, but are largely unusable. Finally, the future work needed in this problem area is elaborated.