doubt about local and remote engineID...?

Hi All,

   I am using net-snmp-5.3.0.1. I have very basic doubt about
engineID's. Which goes as below.
   From net-snmp documents I found out few things about engineID. 

   (1) if u put some command say : 
       rwuser    ---> in /usr/local/share/snmp/snmpd.conf
      createUser myuser MD5 "mypassword" DES password   ---> in
/var/net-snmp/snmpd.conf. 
      when you enable snmpd I can see that password and username gets
encrypted. At the end of the file(/var/net-snmp/snmpd.conf) I can see a
line which contains
    oldengineID 0x800100023 (some system generated hex value).

   (2) Also I got another configuration say
         engineID 0x0120304050 (some valid hex value) in
/usr/local/share/snmp/snmpd.conf and
        If I put 
       createUser -e 0x0120304050 myuser MD5 "mypassword" DES password
in /var/net-snmp/snmpd.conf.

   for both of the above cases I cud successfully query and get
response.  Now my doubt goes as below:

  (1) Out of above two which is the local engineID and which is remote
engineID. plz let me know if there is some other engineID configuration.
  (2) whats the need or use of these local and remote engine ID.


Thanx in Advance.

Regards,
Raghavendra. S