Use Cases are meant to showcase your achievements, the good you do and the improvements you have made (e.g. in regards to your operations or the chemicals used). Talk about how you have overcome hurdles in implementing the ZDHC Chemical Management System (CMS) Framework and Technical Industry Guide (TIG) or other ZDHC guidelines. Even topics that are not in the scope of the ZDHC guidelines can be covered.
Have a look at the existing Public Use Cases to get inspired!