When you manage several projects, some of them may be related. You may have some task start and finish dates in one project that depend on the start and finish dates of another project. Or, you might want to make sure that a resource assigned to tasks in two separate projects isn’t assigned to work on those tasks in both projects simultaneously. One task shouldn’t start until the other is finished.
To model dependencies between projects in the same consolidated project file — or between different project files — you can link tasks between projects.