are cursors necessary?

In the program testlibpq.c, these five SQL statements are executed:

    res = PQexec(conn, "BEGIN");
    res = PQexec(conn, "DECLARE myportal CURSOR FOR select * from pg_database");
    res = PQexec(conn, "FETCH ALL in myportal");
    res = PQexec(conn, "CLOSE myportal");
    res = PQexec(conn, "END");

Is this just to illustrate how to create transactions and cursors, or is there
some material difference between trimming the program down to just:

    res = PQexec(conn, "select * from pg_database");

Is there any value in my own query-only programs to declaring the cursor
for each search?

Many TIA,
Mark

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Mark Harrison
Pixar Animation Studios