The type of access path maintenance to specify depends on the number of records and the frequency of add, delete, or update operations on the file while it is closed.
You should use delayed maintenance for files that have relatively few changes to the access paths while the file members are closed. Delayed maintenance reduces system overhead by reducing the number of access paths that are maintained immediately. It might also result in faster open processing, because the access paths do not have to be rebuilt.
You might want to specify immediate maintenance for access paths that are used frequently, or when you cannot wait for an access path to be rebuilt when the file is opened. You might want to specify delayed maintenance for access paths that are not used frequently, if infrequent changes are made to the record keys that make up the access path.
In general, for files used interactively, immediate maintenance results in good response time. For files used in batch jobs, either immediate, delayed, or rebuild maintenance is adequate, depending on the size of the members and the frequency of changes.