a question about exec_simple_query() - Mailing list pgsql-hackers

Hi, everyone:
    In functin exec_simple_query(), why we run a simple query wrapped in a portal.
    For instance:
    version 8.3.0 ,postgres.c, Line 908
    /*     * Create unnamed portal to run the query or queries in. If there     * already is one, silently drop it.
*/   portal = CreatePortal("", true, true);
 
    ......
        In other words, what's the benifit we use a portal to run a simple query?

    Thanks for your help!  :)