The toggle is disabled by default whenever there is a game patch, content patch, or expansion. If you enable the toggle or the CVar gets enabled, which you can change as per Dridzt's suggestion, it will stay enabled until you either disable the toggle or change the CVar.
- Game patch: xx.xx.YY
- Content patch: xx.YY.xx
- Expansion: YY.xx.xx
The toggle stays off until you enable, and stays on until you disable unless one of the list above conditions is true, in which case Blizzard disables the toggle automatically.