This setting is to tell bot which pairs featured in the calendar the bot needs to monitor. Bot is utilising Exness Broker and Forex Factory as calendar sources.
In both Exness and Forex Factory, they feature many pairs within their calendar eg. CNY, USD, EUR, GBP, CHF, etc.
You can tell the bot to listen to particular calendar pairs eg.
EURUSD;USDCHF;GBPUSD
This means, when there are EUR, USD, CHF and GBP news, bot will stop trading or perform other action such as keep trading with smaller lot size, etc.
If you decide to use calendar control, you MUST use this setting.