What is 'query_id' used for when creating schedule plan through the API?

[ogarza]

I've created a subscription to a look, a dashboard, and a lookml dashboard and this query_id field is empty in all three cases, yet the documentation states that a query_id should be provided.

To create a scheduled plan, you MUST provide values for the following fields: name and look_id, dashboard_id, lookml_dashboard_id, or query_id and cron_tab or datagroup and at least one scheduled_plan_destination

I have not been able to find any information on how a query_id relates to a subscription?

In which cases would query_id be populated, or need to be specified when creating a schedule?