Benefits of the company would include and not limited to:

Materia Melding Efficiency: (doing each other's materia melding because of DoH requirements). Example would be you're a specialized blacksmith but you need materia melded to your lance because it requires a LvL "XX" carpenter (and you're only going to use it for 5 levels but you want that awesome crit rate anyway). Instead of leveling up the skill you could ask a carpenter to do it for you while you provide the materias needed and a "thank you" or vice versa.