The purpose of reblocking is to make the most efficient use of available space. If you use DFSMShsm as the data mover and specify the CONVERSION parameter of the SETSYS command, DFSMShsm can reblock some types of record organizations of physical sequential data sets during recovery.
If you use DFSMSdss as the data mover, specify CONVERSION(REBLOCKTOANY) to reblock physical sequential and partitioned data sets.