Per Oracle Help Center, please see the snippet below.
BY SESSION:
In earlier releases, BY SESSION caused the database to write a single record for all SQL statements or operations of the same type executed on the same schema objects in the same session. Beginning with this release of Oracle Database, both BY SESSION and BY ACCESS cause Oracle Database to write one audit record for each audited statement and operation. BY SESSION continues to populate different values to the audit trail compared with BY ACCESS. Oracle recommends that you include the BY ACCESS clause for all AUDIT statements, which results in a more detailed audit record. If you specify neither clause, then BY SESSION is the default.
Note:
This change applies only to schema object audit options, statement options and system privileges that audit SQL statements other than data definition language (DDL) statements. The database has always audited BY ACCESS all SQL statements and system privileges that audit a DDL statement.
BY ACCESS:
Specify BY ACCESS if you want Oracle Database to write one record for each audited statement and operation.
Note:
If you specify either a SQL statement shortcut or a system privilege that audits a data definition language (DDL) statement, then the database always audits by access. In all other cases, the database honors the BY SESSION or BY ACCESS specification.
For statement options and system privileges that audit SQL statements other than DDL, you can specify either BY SESSION or BY ACCESS. BY SESSION is the default.
WHENEVER [NOT] SUCCESSFUL:
Specify WHENEVER SUCCESSFUL to audit only SQL statements and operations that succeed.
Specify WHENEVER NOT SUCCESSFUL to audit only statements and operations that fail or result in errors.
If you omit this clause, then Oracle Database performs the audit regardless of success or failure.
