When Sync mode is enabled, grading operations (including dragging and dropping) are applied to the respective destination eye. For example, grading data dragged from a Right Eye layer is always applied to a Right Eye destination layer, even if it is dropped on the Left Eye. See Synchronizing the Left and Right Eye.
Shots can still be graded separately when Sync mode is disabled. After grading one eye, grading data can be copied to the other eye. See Copying Elements. Separate grading can also be used to differentiate the grades on each eye.
During secondary colour grading, you can copy different grading data for each eye at the same time from one secondary layer to another, and the grading data for each eye that was applied when Sync mode was disabled will be copied to appropriate eyes.