Create index privilege

i want to know when does CREATE INDEX priv. is given.

For Eg.
i have these roles on user1 and no other privs on this user
CREATE ANY SYNONYM
CREATE SESSION
CREATE TABLE
CREATE VIEW
DROP ANY SYNONYM
SELECT ANY DICTIONARY

But im able to create index for user1, how it is possible?
Does CREATE TABLE gives permission to create INDEX?

And we have grant CREATE INDEX to username; syntax when does this will be useful?

If you have CREATE TABLE and the appropriate quota on the tablespace, you are automatically given the privilege to create a conventional index in your own schema.

Check Prerequisites for CREATE INDEX for additional information.