Public Function Add( _
   Optional ByVal Name As Variant _
) As Group

If there is anything in the select set when you add a group to the collection, the contents of the select set will be added to the group. If the select set is empty, an empty group will be created. The contents of the select set are associated with the active sheet. So if you add a group based on the contents of the select set, that group will be added to the active sheet, regardless of the owner of the Groups collection. For example if Sheet1 is the active sheet, and items from Sheet1 have been added to the select set, if you call Sheet2.Groups.Add(), the new group will be added to Sheet1. If you want to copy items from the select set on one sheet to a group on another sheet, after adding items to the select set from the first sheet, call the Activate method on the second sheet, and then add the new group. Empty groups are always added to the sheet that owns the Groups collection.

Groups Collection  | Groups Members