This means that you can add/readjust the colors, shadow, and highlight effects (LUT’s) to achieve a specific style look or the mood of it. Just like using ColorCorrection but way more advanced!
As for right now (not the final), we have only one option for the tonemapper preset, called ‘Retro.’ This means that the Technology Lighting Compatibility might going to be removed soon as far as I know, but it will keep the same color lighting style as part of the color grading.
(btw I’ve asked for this feature a while back!)