To determine whether you should break up a large project into a master project and Subprojects, consider the following:
Several people can own and manage different parts of the program schedule at the same time - Most of the time, a project file is owned, managed, and modified by a single project scheduler. But often a project schedule will become or has become so large that many schedulers are needed to manage it. Microsoft Project only allows a single user to access a file at a time. By breaking down a large program into Subprojects, different schedulers can own and operate different sections of the schedule simultaneously and independently.
Your project is very large and detailed - If your project contains more than a few hundred tasks, breaking it into Subprojects can make it easier to manage. If some parts of the project contain work that is broken down into more detail than others, it may make sense to make those parts into Subprojects so that most users see only a rolled-up description of the Subproject, but interested parties can view it in more detail.
Your organization is not centralized - In a decentralized or distributed organization, a Master Project and Subprojects give workers more control over their own work than one centralized project file does.
You work on multiple projects - Project managers may have a set of projects they work on all the time, whether the projects are interrelated or not. Instead of opening them one by one, you can open all the Subprojects at the same time when you open the Master Project. This approach also makes it easier to generate reports on multiple projects. If the projects are interrelated, the project manager can create Handoffs, or task dependencies, between tasks in different projects. Creating Handoffs between projects makes it easier for different project schedulers to see how work by other project schedulers affects their schedules.
Your project has multiple stakeholders who care about different parts of the project - When people want to look at different details, project managers can put all the project files on a server and customize different views for various stakeholders. The same project file can be used as a Subproject in different master projects to customize the information displayed.
