When to use Sub-Projects and when to use Project Tasks

[phil_bool_unifi]

I appreciate this is something of a subjective issue, but I'd like to get your opionions on this:

Given that, in the new (and awesome) project workspace, you can now see the tasks in a Sub-Project in your Project Planning view, when would you use a Sub-Project instead of using a Project Task with child tasks?

For me, anything within a project, managed by the same person and driven from the same parent data should be a project task, but some of my customers have very strong feelings about this, and I'm wondering if I'm more isolated in my opinion about this.  

How do you decide?

[M Iftikhar]

Hello @phil_bool_unifi,

In my experience, the decision mainly depends on how independently the work needs to run. If it shares the same project manager, budget, resources, governance and it logically fits within the same delivery flow, then we keep it as a Project Task with child tasks. With the new Project Workspace now surfacing Sub-Project  directly in the planning view, there’s even less operational need to break things out.

We typically reserve Sub-Projects for scenarios where the work really functions like a small standalone project: its own schedule, dependencies, approvals, or a different delivery team. In those cases, treating it as a Sub-Project makes the structure and reporting cleaner.

That’s what I’ve seen work well, though PMO preferences can vary quite a bit.

If my response helped, please mark it as the accepted solution so others can benefit as well.

[M Iftikhar]

Hi @phil_bool_unifi,
If this solution helped, please consider marking it as accepted solution to support the community. 

[Marcos Gianoni · Accepted solution]

The Decision Framework: Sub-Project vs. Child Task

The decision is not based on visibility, but on scope, governance, financial tracking, and resource management.

Criterion	Use Project Task (with Child Tasks)	Use Sub-Project
Scope & Dependency	Work breakdown entirely internal to the parent project's success.	Represents a separate, distinct initiative that is required for the parent project, but could potentially stand alone.
Governance & Approval	Requires no separate governance, status reviews, or approval workflow beyond the parent project.	Requires separate status reporting, its own lifecycle (e.g., separate approval, closure), or is managed by a different Project Manager (PM).
Budget & Cost Tracking	Costs are aggregated and tracked solely at the parent project level.	Requires independent financial tracking, its own budget, or separate Cost Plans for granular reporting.
Resource Allocation	Resources are allocated and tracked under the parent project's resource plan.	Requires a separate, dedicated Resource Plan that needs to be managed and fulfilled independently from the parent project's resource pool.
Project Management	Managed entirely by the Parent Project Manager (PM).	Managed by a different PM or requires a high degree of autonomy.

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Best Practice Guidance in ServiceNow SPM

When to Use Project Tasks (with Child Tasks)

This is the standard, preferred method for simply breaking down the work within a single project.

• Work Breakdown Structure (WBS): When you are purely building the WBS—Phase $\rightarrow$ Task $\rightarrow$ Sub-task—use Project Tasks. This keeps the project cohesive and easy to manage by a single PM.

• Simple Roll-up: When you need a simple, reliable roll-up of effort, cost, and progress directly to the parent project.

• Example: In an "HR System Implementation" project, creating child tasks like "Configure Access Roles" or "Develop Training Documentation" under a parent "UAT Phase" task.

When to Use Sub-Projects (Project-to-Project relationship)

Use Sub-Projects when the work represents a significant piece of the puzzle that needs to be managed like a standalone project.

• Integration/Vendor Management: If the work is being executed by a separate team (e.g., an external vendor, a different department like Infrastructure), and they need their own Project record to manage their team, risk, and budget.

• Different Project Methodology: If the parent project is using Waterfall, but a specific stream of work (the Sub-Project) needs to use Agile or Hybrid methodology, a Sub-Project allows for independent configuration.

• Financial Segregation: If the funding source dictates that this portion of the work must have a completely separate financial record from the parent.

Conclusion

Your opinion is aligned with ServiceNow best practices:

Anything within a project, managed by the same person and driven from the same parent data should be a project task.

If you can avoid the overhead of creating and managing a separate Project record (with its own budget, resource plans, and governance), you should use a Project Task with child tasks. Reserve the Sub-Project for cases where a separate, independent management layer is truly required.

[phil_bool_unifi]

Thanks, both.  @Marcos Gianoni , I really appreciate the time you put into that - it was very helpful.  Definitely better than just asking AI. 
@M Iftikhar , thanks for sharing your experience - I feel like we're on the same page.