The stereo offset control in the RotoPaint properties allows you to move the selected stroke/shape on the x and y axes. This is an extra transform that is applied after all other transforms. Typically, you would position the stroke/shape correctly in the hero view, then split stereo offset, and drag the stroke/shape to its correct location in any other views. Note that you can also press Shift while dragging to constrain the movement to the x or y axis only.
Stereo offset can be useful, for example, if you have a stroke/shape that is correctly positioned in one view and you want to move it to its correct location in another view, but can’t use the translate control on the Transform tab because that’s being driven by Tracker data.