We tried to use Sub-Projects because we had many use cases but I have since made it a rule to not use them. Resource Plans became such a nightmare to manage because it all rolls up to the parent project. It made resource planning confusing and ineffective. Now I am hoping that with the new Resource Assignment piece this might be improved, but we are waiting until the May store release for trying the new resource stuff.
Overall having the one gantt view that included the sub-projects project plan was the best win, but I was not willing to sacrifice the resource planning. That is just us though and our experience.
