This list is shared. Enter the same code on another phone and you'll both see every change.
Anyone who knows the code can read and change this list. Stopping keeps your copy on this phone.
Use one code on both phones and you'll share a single list — add on hers, it appears on yours.
Whatever is on this phone now gets merged into the shared list. Anyone who knows the code can read and change it, so keep it between the two of you.