Either to a schedule (like wake up calls) or based on a command line command (like how you can do with ‘call flow control’)
Use case: For an elderly member of the household to be able to use a physical push button to send an MQTT command to the host Pi that causes an extension to ring. When the extension is answered, it begins dialling a preset number.
Pretty much every single click-to-dial utility works this way. You ORIGINATE a call to the local extension which then bridges to another channel on answer.