The benefits that DBCTL offers in the area of performance are:
Previously, if you did not use DBCTL, DL/I code and its associated control blocks (including DBRC) resided in the CICS® address space. With DBCTL, all this is moved out of the CICS address spaces, freeing virtual storage within CICS systems that previously contained local DL/I.
Because the components of the CICS-DBCTL interface reside in separate address spaces and, because DBCTL uses a separate task control block (TCB) for each application thread, throughput on multiprocessors is improved and there can be more concurrent activity. See Tuning a CICS-DBCTL system for more information on thread and TCB performance considerations.