This is for stereo vision, structure-from-motion computations and so on (i.e. figuring out the geometry of what you're looking at from photos).

Every lens that is manufactured is slightly different, and has a slightly different ray-in-space to pixel mapping that these tools help you obtain.

Care to elaborate?

All lenses have some innate distortion. In good lenses it can be hard to see, sometimes, but its there. Manufacturers use tools (maybe like this one?) to analyze their lenses during design as well as after production for consumer models and create corrective models.

So when I take RAW files from my canon DSLR and load them through a compatible raw processing software, it knows the lens and camera used to take the picture and it will correct those distortions, and sometimes deal with chromatic aberation etc.

This person said it better than I.

We would write pipeline modules that could calibrate for specific lenses (think chromatic aberration and vignetting).