No, you do not need expander unless if you need those zones physically. OpenSprinkler allows you to set more zones than there are physically, because a zone can be a ‘virtual zone’, such as you can set it up as HTTP zone, remote zone, RF zone etc. In your case, the dummy zone is just used to activate the master zone. If you do not want to see those unused zones on the screen, you can disable them — click the ‘gears’ icon next to a zone name, and click ‘disabled’, that way it will be hidden from the UI.