An example would be configuring a 1724A label so that the data for each field does not need to be entered every time before printing.
There are a few ways to do this depending upon your requirements.
If you never need to change the data for a particular field you can change the data source for that field to "Formula" and then set the formula to the required fixed string.
If you never need to change the data for a particular field and that field's data is only displayed in the PDF417 symbol, you can change the appropriate field reference in the PDF417 symbol's formula to the required fixed string.
If you may need to occasionally change the data for a particular field, you can set a clear value for that field. In this case you can change the data at print time if necessary.