Do see the other threads on this :) From those threads, there are two points - point 1, the gamma was added for technical reasons to adapt to the new OCIO / Color Management in Max and C4D, until we changed Corona to be compatible with that new functionality; the technical gamma was removed once Corona was compatible. Point 2, we'll be adding Gamma, Gain, and Lift to tone mapping, as the artistic gamma, as people had started using the one added purely for technical reasons as an artistic control (not its intended use), and this will be in Corona 12.