startSetup() and endSetup()

Ever wondered what they do? Basically they disable and then enable foreign key checks, and set the SQL mode to NO_AUTO_VALUE_ON_ZERO, then back to the old SQL mode. Below is the code taken from Varien_Db_Adapter_Pdo_Mysql:

/**
 * Run additional environment before setup
 *
 * @return Varien_Db_Adapter_Pdo_Mysql
 */
public function startSetup()
{
    $this->raw_query("SET SQL_MODE=''");
    $this->raw_query("SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0");
    $this->raw_query("SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO'");

    return $this;
}

/**
 * Run additional environment after setup
 *
 * @return Varien_Db_Adapter_Pdo_Mysql
 */
public function endSetup()
{
    $this->raw_query("SET SQL_MODE=IFNULL(@OLD_SQL_MODE,'')");
    $this->raw_query("SET FOREIGN_KEY_CHECKS=IF(@OLD_FOREIGN_KEY_CHECKS=0, 0, 1)");

    return $this;
}