The purpose of the Roadmap module is very simple. While the Gantt is a Waterfall tool concerned with specific dates and resources, Roadmap contrasts it by being Agile and focusing on Teams. This screen allows you to roll up mulitple Sprints and see how they stack against each other. What is each Team doing in those Sprints? What are the cross-Sprint dependencies?
As the title suggests, Roadmap is fully compliant with The Scaled Agile Framework™. As a result, it uses SAFe-related terms. If any of them is unclear, we encourage you to read more here.
There are plans to also release the Roadmap as a separate plugin, in case somebody would like to have it without the Gantt, Resource and Risk management.