Winter mode is the default setting for systems after their creation, and the most important of those in the app; in fact, winter season is the one that allows the system to heat the house.
Whether you have a stand-alone or a central heating system, Winter mode is the correct setting for switching the heating on/off, and modulating it (Menu - Settings - Season).
Basic winter operation involves starting the heating when the temperature detected by the devices falls below the setpoint (desired room temperature):
in stand-alone systems, the heat generator is activated by a wired and app-configured device (Smart Thermostat or Starter),
in centralised systems, Smart Valves modulate the opening and closing of hydraulic valves,
the WiFi smart electric radiators are programmed to heat only in Winter mode.
To find out how the system works in summer mode, read here.