Only Tamron Adaptall lenses can use it, and only they need it. You can't fit the lens to a camera body without the adapter.
I believe Tamron had earlier versions, but the one I remember (from the 80s) is the Adaptall-2 system.
Rather than make custom fit lenses for all the different SLR mounts available then (there were MANY!), Tamron made one lens mount that fit onto the Adaptall-2 adapter. The adapter then fit onto the SLR's lens mount. Change adapters, and you could fit the same lens to a different brand SLR.
The adapter is not a teleconverter, nor is it an extension tube. It allows you to mount the lens to the body, and provides mechanical linkages between body and lens (iris control).