How user friendly it is and how our entire team quickly adopted it. It works well both for a management perspective (overview, capacity, progress, utilisation of ressources) and for more operationnal roles (to do, prioritization, project time monitoring etc...).
Fore us a key aspect of such a tool is to have both a solid and usable time tracking solution and a complete project management suite. Forecast handles both beautifully.
Project management and our agency ressources/capacity management.
We are also using it to handle our dev and product team; sprint mode is really helpfull and we've been able to improve our TTM efficiency.