In some cases you need to know in which your file is located. For example: you distribute several files and one workbook opens another. If you file is converted to application, ThisWorkbook.FullName call does not help. It will point you to file in TEMP folder. To get right path you should use LockXLSRuntime.GetApplicationPath method.
LockXLSRuntime.GetApplicationPath( <Workbook Object> ) returns folder, where application file is located.
If this method is called from usual Excel file (locked or unlocked), it returns folder of the ThisWorkbook.FullName file.
Example of the VBA code, which uses this method: