Why vacumming performed on template1 with initdb command ?

Respected,

Am in PG 9.0.4.
While creating a new cluster with "initdb" command I observed a statement
echoing as "vacuuming database template1.... ok".
Why vacuuming is performed on a new cluster on template1 database.
Please share your valuable comments.

*Initdb output:*

[postgres(at)test-psql01 bin]$ ./initdb -D /u01/pg/update_test_data
The files belonging to this database system will be owned by user
"postgres".
This user must also own the server process.

The database cluster will be initialized with locale en_US.UTF-8.
The default database encoding has accordingly been set to UTF8.
The default text search configuration will be set to "english".

creating directory /u01/pg/update_test_data ... ok
creating subdirectories ... ok
selecting default max_connections ... 40
selecting default shared_buffers ... 32MB
creating configuration files ... ok
creating template1 database in /u01/pg/update_test_data/base/1 ... ok
initializing pg_authid ... ok
initializing dependencies ... ok
creating system views ... ok
loading system objects' descriptions ... ok
creating conversions ... ok
creating dictionaries ... ok
setting privileges on built-in objects ... ok
creating information schema ... ok
loading PL/pgSQL server-side language ... ok
vacuuming database template1 ...ok
copying template1 to template0 ... ok
copying template1 to postgres ...ok

WARNING: enabling "trust" authentication for local connections
You can change this by editing pg_hba.conf or using the -A option the
next time you run initdb.

Success. You can now start the database server using:

./postgres -D /u01/pg/update_test_data
or
./pg_ctl -D /u01/pg/update_test_data -l logfile start

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Regards,
Raghavendra
EnterpriseDB Corporation
Blog: http://raghavt.blogspot.com/