This feature allows you to create a group access field. Using this field you can organize your workspace much easier.
At first navigate to the workspace list as a sitecollection administrator and click in the "Collaboration Manager" Ribbon Group.
Choose the workspace which should have a "group access field" and click the button "Group Access"
In the Configuration dialog you can fill in the generals like name, description, the contenttype to be assigned to and the require column information.
The Target group box is the displayname of the group in the workspace, where all selected groups will be assigned to. Please spell-check after filled in.
The Preselected Groups are available for user selection in the forms of the assigned contenttype. If you select "fix checked" then the group will be checked by default, but can be unchecked by the user.
"Lockable Groups" creates the option to remove all people and groups of this workspace. For this option you have tou use the Locked Workspace Field.
Wait for the dialog.
The field is added to the Workspace(s).
To check the function go to the site settings and control if the users are really added.