Over time, you might join several Office 365 tenants as a guest. Some of those Azure AD guest accounts probably won’t be needed forever and you want to clean them up. This is easy for individuals to do through their MyAccount page, which might just be a page that they never knew existed.
Security groups are often used to protect access to resources, but they can’t be used to control membership for Microsoft 365 Groups or Teams. If you want to use AAD security groups to control membership for Groups and Teams, you need to come up with a way to synchronize. PowerShell is available to do the job, and as it turns out, it’s not too difficult.