The cell origin is important for a cell because this point is the instantiation anchor for cell instances. The cell origin adjustment function allows shifting the origin to a certain place relative to a cell's bounding box. This can be either the center, a corner or the middle of an edge of the bounding box. The bounding box can either be computed from all or just from the visible layers.
If the "Adjust instances in parents" check box is clicked, the instances of the cell will be adjusted in the opposite direction. Hence, the cell effectively does not change, but locally the origin of the layout will be shifted.
The cell origin adjustment function can be found in the "Cell" submenu of the "Edit" menu.