With even field dominance the edit or switch occurs at the start of the even field (some equipment, such as vision mixers or switchers allow the field dominance to be set to 'none' which means the switch will occur on the next field boundary after the switch has been pressed).
With balanced field control, the edit or switch takes place at the beginning of the even field (certain devices like vision mixers or switches allow setting field dominance to 'none,' indicating that the switch will happen on the next field boundary after pressing a button).