As the names imply, like a ceiling fan/light combo where the fan is to be controlled by the pull-chain (unswitched live), while the light is to be controlled by a wall switch (switched live). If the two neutral terminals are common, you only need use one.
Unswitched Live is always providing power (charging) battery back ups. When that power is lost battery knows to turn on give however many watts for 90min.. The switched live is so you can use it as a regular light without a 24/burn
.. Not all EM lights have to be on 24/7..