In general, the use of exit routines is optional. An RPL exit routine is an alternative to having a routine that is branched to in the mainline program following the posting of an ECB by VTAM®. Refer to Using RPL exit routines for a discussion of these two alternatives. Most EXLST exit routines are optional, though some are designed for common use and should be included in an application program. The LOSTERM, NSEXIT, SCIP, and TPEND exit routines are strongly recommended because, without them, the application program might not be notified of certain important events. The SCIP exit routine is required by any application program that acts as a secondary logical unit (SLU).

The RELREQ exit routine is required only if the application program is to be notified when another logical unit (LU) requests a session with an LU that is in session with the application program and is at its session limit.

If an EXLST exit routine is not provided and the event or condition that the exit routine would handle does occur, the application program may never be informed about the event or condition. In some cases, the application program might learn of the event or condition through return codes or information in an RPL when it is posted complete.