The choice on whether to use reducers on the edge of a balcony rooftop is up to you. Normally the reducers are used on ground level situations to avoid any danger of tripping on the edge of the deck area and also to hide the view of the plastic base.

With an elevated deck, neither of these situations typically apply.  However you may decide that the reducers give a neater finish to the edge of a balcony as illustrated in the picture below.