You have a symbology for a layer that's complex and broken out by attributes. You get in new data with different attributes, but you want to use the same symbology. I wish there was a way to change the field /attributes you want to use for that symbol without having to save the symbol, add the data, set the new fields, add the attributes and then go find the symbol you saved.
With this, you could take your old mxd and apply new data to it quickly. It would really help with the Templates, especially the Community Map Template. It would also save people from having to use ETLs or Data Interoperability to import data to a new model to support your mxds.