I think Andrew is suggesting that there are three possibilities for this setting, not two. Will gave instructions for turning the setting on and off. Andrew gave instructions for reverting to the default value, which may change in the future.
In other words, if you draw turning LeaveEmptySelectionEmpty on and decide it isn't for you, then you should probably remove the setting rather than turning it off. Removing the setting means that you'll see future improvements in this area. Turning it off might hide such improvements.