No, converting units is not a useful exercise. airplanes are measured in mm - even the full length is in mm not decameters or even hecameters (i had to look those prefixes up, spellcheck doesn't even know the word, but I think they are correct)
Vehicle drawings (maybe mechanical engineering in general) might be in millimetres, but a lot of civil engineering works in metres, so when designing some bit of infrastructure to fit certain kinds of vehicles, I do need to convert between the two, and the easier, the better.
