In my case, the workflow, for whatever reason, is that a user will select features from a shapefile using several methods (graphic select, select by other features, select by attribute) and once satisfied with the selection set, will then run a tool that calculates a field for only the selection and then needs to run a frequency on the full set of data (nothing selected)... in order to clear the selection, gotta use selectlayerbyattribute clear_selection option which requires a layer. So, the shapefile, with its selection, has to be converted to a layer, which will only take the selections into the layer, all unselected data is lost.