Subprojects allows you to create hierarchy of JIRA projects. Once you have created project hierarchy you can use new project picker tree to select a project on new issue dialog, you may use project in subprojectsOf() JQL to query issues or use subprojects dashboard item to add high-level view of project hierarchy into any dashaboard

How you will group your projects is completely depend on your organizations. Here some different grouping alternatives:

  • You may create a group for different project categories, for example "Service Desk Projects", "Business Projects", or "Software Projects"
  • You may create a group for different organizational divisions, for example "HR Projects", "Finance Projects"
  • You may create an Archived category for inactive projects
  • You may create categories for internal projects or customer projects
  • You may even create multiple child projects for a complex project and group child projects under the main complex project. 
  • You may create different groups for "Hardware Projects" and "Software Projects"