Open any file in your project, such as a drawing file or an assembly file. Invoke the command from the tools menu. You will be able to see a tree representation of every file referenced directly or indirectly by the current file. Picking on any item in the tree will allow you to browse the properties and even edit them without leaving your current file. You can even edit the virtual items in your assemblies.
Switch to batch mode, pick the files that you want to edit and then set your standard and custom iproperties for all the selected files in one operation. You can also remove user defined properties from all files.