If you do not do this, you may receive an application error (with error messages WF0096 and WF0100) when the changed screen would have been displayed. When a screen is submitted and there has been a change in the input buffer definition you may see a MCH1236 error from/to QWSGET in the user job. To fix either of these problems you will need to ensure that the version of DDS source that the display file object was created with is the same as the version of DDS source that was converted for the WebFacing application. If the green screen version of the application is working fine then simply reconvert the DDS members that have changed.
This problem can also occur if more than one DSPF object with the same name is used. In this case, the DSPF Object Mapping will need to be manually updated to explicitly define the library in the mapping for the multiple DSPFs, rather than using the default /DSPF-NAME mapping.
Sometimes this error will also occur if the publishing failed to finish successfully. To fix this, stop the application server, republish the project, and start the application server again.