The Graf Zeppelin never completed. The ship was about 70 - 80% finished when work was halted. Aircraft for the carrier had already been produced (the Me 109t, Fi 187, and Ju 87t). These were pressed into service in various other roles after the carrier was not going to be completed. The Straßer was not that far along and was broken up when the KM stopped its construction.
As for their actual use in service, who knows? A single carrier was really not of great value. Several could have made a big difference if used properly. But, then again, the Germans never were a really successful seapower.