Thanks for getting back to us, systematicbookke.
I can help share some insights regarding Sub-customers or Projects features for your business within your QuickBooks Online account.
In Projects, there can only one hierarchical level which means it can't have sub-projects. Unlike customers wherein you can have a project or multiple projects. Also, Projects needs you to bill the project with the customer, whereas sub-customers can have a different billing address than the customer.
I've listed below the advantages of utilizing Project:
Check out our detailed guide on changing sub-customers into projects.
Feel free to comment down below if you need anything else.