The UI presently presents very little means to enable selection of objects which have been made unselectable -- users must basically resort to searching by hand, possibly through the entire outliner tree.
This addition to the filters will allow the user to enable the outliner tree to restrict the listing to only Selectable objects, which may serve some use itself, but in accordance with Nathan Craddock's discussions with the UI team, is primarily intended to be used along with a future-planned Inverse [of the filters] option, so UNselectable objects may be easily found in the outliner.