The obsession with the industrial infrastructure was largely based on the hypothetical concept of invasion/occupation… what resources could the US military convert to wartime use? What resources could the Soviet army utilize for troop support? Etc., etc. It was a very “pie in the sky” idea, and not terribly realistic, but a possibility they wanted to account for all the same. They had better records in terms of transportation capabilities than we did, with notations such as bridge load ratings, which would be useful for knowing what type of military vehicles could use what bridges for crossing, things like that. The data was more relevant and extensive than one might initially assume, and really gives understanding to the depth and breadth of their surveillance activities.