Circuit-switched backbone networks are appealing especially due to their low switching cost. However, some of their links may be poorly utilised with respect to the available capacity. Grooming can be used to improve this utilisation: optically switched lightpaths are groomed in fibres using WDM, and flows are groomed in lightpaths using TDM. However, grooming require more transmission resources if lightpaths/flows are not following the shortest-path and take detours. It can thus be counterproductive.