Not necessarily a spy tool.
1. The military always appreciates an accurate map, especially one of cramped hostile quarters. They clear a building or tunnel and then map it out. That way, if enemies try to use it again, instead of flying blind, they can look at the map and find the best places to coordinate assaults.
2. The mapping tech is supposedly 3D, 360 degrees, and automatic, meaning you just have to walk through the place to get a picture. Bit faster and more accurate than a webcam bot (and the tech doesn't even preclude loading it on top of a rover for recon).
3. Such plans may not exist (especially if the building is improvised). Neither may the architects/builders (who may have fled or be dead). Also, the building may have predated CAD or may be in a technologically-backward location, meaning a computer version of the plan wouldn't exist, either.
4. Either the tag end of a clearance team (you would use the thing AFTER an area is clear) or loaded on a rover (who probably wouldn't care either way about the load).