Do We have Clusters or IOT?

In Tom kytes's book "Effective Oracle By Design", it has been mentioned
that Steve Adams(http://www.ixora.com.au/) said, "If a schema has no IOTs
or clusters, that is a good indication that no thought has been given to
the matter of optimizing data access."

Checking our production DB, find only SYS schema has clustered tables.

1 select cluster_name, owner, table_name from dba_tables where
cluster_name is not null
2* order by cluster_name

system@PRDP> /

CLUSTER_NAME OWNER TABLE_NAME
------------------------------ ------------------------------
--------------------------
C_COBJ# SYS CDEF$
C_COBJ# SYS CCOL$
C_FILE#_BLOCK# SYS SEG$
C_FILE#_BLOCK# SYS UET$
C_MLOG# SYS MLOG$
C_MLOG# SYS SLOG$
C_OBJ# SYS ICOL$
C_OBJ# SYS COL$
C_OBJ# SYS TAB$
C_OBJ# SYS ICOLDEP$
C_OBJ# SYS REFCON$
C_OBJ# SYS LIBRARY$
C_OBJ# SYS NTAB$
C_OBJ# SYS TYPE_MISC$
C_OBJ# SYS LOB$
C_OBJ# SYS VIEWTRCOL$
C_OBJ# SYS ATTRCOL$
C_OBJ# SYS COLTYPE$
C_OBJ# SYS IND$
C_OBJ# SYS CLU$
C_OBJ#_INTCOL# SYS HISTGRM$
C_RG# SYS RGROUP$
C_RG# SYS RGCHILD$
C_TOID_VERSION# SYS TYPE$
C_TOID_VERSION# SYS
COLLECTION$
C_TOID_VERSION# SYS ATTRIBUTE$
C_TOID_VERSION# SYS PARAMETER$
C_TOID_VERSION# SYS RESULT$
C_TOID_VERSION# SYS METHOD$
C_TS# SYS FET$
C_TS# SYS TS$
C_USER# SYS USER$
C_USER# SYS TSQ$

No IOT tables either:

1 select iot_name, owner, table_name from dba_tables where iot_name
is not null
2* order by iot_name
system@PRDP> /

no rows selected