The persistent property is used to keep the event instance playing until it is explicitly stopped.
If the persistent option is enabled, it forces an event to continue playing even when it is not producing audio and would otherwise stop.
If the persistent property is not enabled an event will stop on its own if no instruments are triggered and the playback position of the timeline is beyond the end of the timeline (i.e. beyond the end of the last marker or instrument trigger region).
It’s useful for when you have gaps in an event that only has instruments in a parameter sheet. Previously the event would stop if it detected no audio output, but with this property enabled it will not stop.