Pretty straightforward, this serves as a separate theme similar to the existing dark theme except the background color is purely black (#000000) instead of gray.
Like other AMOLED/black dark themes, it takes advantage of devices with AMOLED screens to reduce energy usage. Not only that but it's also easier on the eyes. If it is implemented, I think it should be in the 'Appearance' settings under 'Theme'. The option could be to the right of the existing dark theme.
