When the situazion allows it, use static variables to avoid running the same code several times. You will thus prevent unnecessary CPU usage.
This is especially effective for resource-intensive procedures.
To only load a heavy-to-load parser once, use static variables:
private function dataParserLoad() {
static $done = FALSE;
if (!$done) {
require_once APPLICATION_PATH_APP . '/ libraries/DataParser/Parser.php';
$this->parser = new DataParser();
$done = TRUE;
}
}