If you are a developer and you set up SharePoint on a VM (Virtual Machine), it is very easy to set up your entire environment on a computer which is not a member of a domain (i.e. part of a Workgroup).
Unfortunately, one of the major problems that you may encounter when doing this is while dealing with Workflows.
Particularly, the Tasks List has a built-in e-mail notification Workflow that sends an e-mail to the individual in the “Assigned To” field of the Tasks List.
As you can guess, in a Windows Workgroup, this e-mail field is never populated because Windows User Accounts do not expose the Mail attribute on the User schema when your computer is only part of a Workgroup!!
Therefore, if you are planning on doing any testing with SharePoint Workflows (especially workflows based on the Task List), it is advised to build your SharePoint developer VM as a member of a domain.