How does Oracle use the parameter GLOBAL_DBNAME in listener.ora ?

How does Oracle use the parameter GLOBAL_DBNAME in listener.ora ? I faced this problem:
Note: The SERVICE_NAMES parameter was set to SFA in the init.ora file File listener.ora is
SID_LIST_JLISTENER =
(SID_LIST =

(SID_DESC =      
        (GLOBAL_DBNAME = SFA)


      (ORACLE_HOME = /home6/sfa/app/oracle/product/8.1.5)

      (SID_NAME = SFAPP)   )  )

File tnsnames.ora on client is
SFTEST.IN.TATAINFOTECH.COM =
  (DESCRIPTION =
    (ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 163.122.32.59)(PORT = 2521))
    )
    (CONNECT_DATA =
(SERVICE_NAME = SFAPP)

    )
  )

When I tried to connect from client I got a error : "Unable to resolve service name". When I commented out GLOBAL_DBNAME = SFA - the connection worked !!! I am trying to understand what was going worng - since the tnsnames and listener was generated
by Oracle utilities.

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Author: TAG DBA
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