The only "benefit" would be having multiples in the marriage bed and "wife" #1 not able to complain. Strange, I don't see that church allowing women to have multiple "husbands".
Having watched the show a few times, I think he might mean multiple people engaged in child care, education and rearing, multiple cooks and cleaning/errand running people, multiple streams of income, the secure feeling of a large family plus what you mentioned. The husband actually sees the multiple beds as something of a headache, but he obviously believes in the tenets of his religion.