The Copy option in the Planning Assistant copies the values from one cube slice, including their distribution on the base level, to another cube slice. If there are already values in your cube, you can use the copy command to read out values of a cube cell and copy them (including distribution) directly into another one.
Copying cell values will not yield the same results as splashing them. Splashing splits the value among the subsequent base elements, while copying maintains the source values of the original elements.
Updated September 27, 2022