Ruenroeng, who will be defending his world title on September 10th against McWilliams Arroyo (15-1, 13), will feel that sparring with Jaro will do him the world of good. Although Arroyo is more adaptable than he Filipino the sparring will give Ruenroeng some time in the ring with a heavy handed and physically strong fighter, much like Arroyo.
For Jaro the idea of sparring with the Thai is likely based around speed. Jaro will be fighting on September 20th against Carlos Cuadras (30-0, 24) and although Cuadras is heavy handed he's actually a fighter who builds a lot of his success on his speed, a trait that he shares with Ruenroeng who is a slick fighter, though their speed is very different in the way they use it.
The training, in Thailand, will serve both men well ahead of their upcoming fights though both will know that their upcoming contests are tough and that neither is guaranteed a victory against their upcoming opponents.