The article explains why they do it. "Since a hero character close to camera felt attractive with a stereo convergence, that would mean the background in the s

The article explains why they do it. "Since a hero character close to camera felt attractive with a stereo convergence, that would mean the background in the same shot would be too extreme and unpleasing on the eye. Instead of dialing down the stereo effect overall, Disney pioneered the use of special camera rigs that would render the foreground with one ‘stereo camera’ or solution, while rendering the background with another. Thus the foreground character would appear round and with more fullness, but their background would appear more relaxed, less stereo pronounced."