5,000 sites say a workgroups are for accessing files between computers and how to create/join one. I cant find a clear answer on what it actually is or how it differs from making a folder shareable on a network?=
Am in the school of a long as it works, why need to know why? YMMV.
I always use a workgroup, but I suspect you don't need it to share files, it just a Microsoft mechanism for the explorer to easily browse groups memberships.