It is a grandmothered group which was created long before groups had charters. Soc.women was created as a very early newsgroup, back in the days when all group names started with net. In the beginning it was called net.women. The flame is invented. Net.women is created.
Men take over the net.women group.
Since there is no charter there is no official purpose. The unofficial purpose depends on whether you are a man or a woman. Nobody reads soc.women. There is one exception. The short answer is - everybody.