Sub-groups allow items on a Gantt Chart to be nested within other items. For example, you could have an item named 'Demo Prototype' within which you would list each individual demo, 'Sales Demo', 'Marketing Demo', Support Demo', etc.
Currently this functionality is only partially supported through the 'Add to Release Phase' drop-down when adding existing Features to a Release.
The limitation we run into is that, in Aha, only defined Features can be nested within other items.
This is also available through the Releases roadmap page, where you can add new features to a specific release or release phase.
On the Releases roadmap page, when scrolling on the Gantt chart, you will see hyperlinks appear to "Add new feature." this can allow you to nest new items into the release phases on your roadmap.