Standard and sub-task issue types must always have their own workflows.

Epics cannot have sub-tasks in a Jira Software project.

There are three levels of issue types in a Jira Software project; Epic, Story, Sub-task.

Sub-task issue types can have a different issue security level than their parent.

An issue type scheme can have unlimited sub-task issue types.

You can disable the Create Sub-task operation on some standard issue types.