The ability to see all your projects in one place, plus you can create custom dashboards for each project so that it's easy when looking at specific issues or tasks within a single view! It would be nice if there was more flexibility with how we could add new views into our dashboard (i think this is being worked out).
We use eositpm as part of managing multiple portfolio items including cloud services/infrastructure management etc - its very good because everything about those areas are managed through here too!!