It would be great if you could set the symbology for the features that are currently selected. This would allow a group of features to be classified based on something other than data without selecting/exporting a layer and would be particularly useful for larger datasets. I am trying right now to use it to mark census blocks that I have QC'ed. The only method that I can think of currently is to set the symbology layer for unique values and manually change the symbology as I finish each block. It helps in symbolozing features as a group that would not normally be grouped together, ie. selecting which areas work crews should be focusing on or houses for sale in an area, without creating a new field or layer.