z/OS calls certain pairs of commands or procedures affinity aspects, and requires each member of the pair to be issued from the same TCB.
Some examples are:
OPEN/CLOSE
If you OPEN a file in one TCB, you must CLOSE it in the same TCB. You can process the file in as many environments as you wish; you simply need to open and close it in a single TCB.
LOAD/DELETE
GETMAIN/FREEMAIN
Language Environment® heap storage, including storage associated with a call to the CEECRHP callable service, will have affinity to the TCB which created the heap. All get and free requests must be done from this single TCB.
A less obvious example is a DB2® table. You can update a DB2 table only in the same TCB in which it was created.