inner join vs for all entries

hi experts,

i have done SQL Trace on select statements using joins and for all entries.

case1: using joins and time taken             : 2.249.936

case2: using for all entries and time taken : 3.074.469

Clearly i can see that join is bit faster than for all entries.But i would like to know in which cases for all entries is faster than joins

and the cases in which joins are faster than for all entries.

i can see data being fetched from only KNA1 table in ST05 but i get data from KNB1 even.Without a fetch on KNB1,how am i getting data from

    KNB1 using joins.??

Please advise

TABLES: kna1.

SELECT-OPTIONS:s_kunnr for kna1-kunnr.

data: BEGINOF it_cust OCCURS0,

       kna1 type kna1,

       knb1 type knb1,

      ENDOF it_cust.

data: it_kna1 typeSTANDARDTABLEOF kna1,

       it_knb1 typeSTANDARDTABLEOF knb1.

*using joins

select * INTO  TABLE it_cust from kna1 INNER JOIN knb1 on kna1~kunnr = knb1~kunnr

                                                        where kna1~kunnr in s_kunnr.

*time taken  : 2.249.936

*using for all entries

SELECT * from kna1 INTOTABLE it_kna1 where kunnr in s_kunnr .

ifnot it_kna1 isINITIAL.

   SELECT * from knb1 intoTABLE it_knb1 FORALL ENTRIES IN it_kna1 WHERE kunnr = it_kna1-kunnr .

endif.

*time taken : 3.074.469