Polygamy is not really that unusual in other cultures ( and possibly wasn't in ours until the import of Christianity about 1500 years ago). Depending on how it's managed and how things are worked out it can work very well. Someone I know quite well was involved in polygamous relationships, and it worked very well for everyone concerned for lots of reasons.
1. a single household where everyone is working obviously has more money than several smaller ones ( bills are cheaper etc).
2.There are no childcare issues as if people are careful about their work times someone is always available to look after the children without the need to send them to creche.
3. There is an inbuilt support system that doesn't just rely on a partner.
etc etc etc.
I think it all depends though on whether the people concerned are happy intelligent well adjusted people or not because for a scenario to work properly everyone has to be equal, largely unconcerned what society thinks about their arrangements and to have left an social conditioning regarding monogamy at the door when they entered into things.
I had a long and interesting discussion with the people concerned about this and came to the conclusion that actually for some people it can work and clearly does, as long as it's viewed as an alternative lifestyle choice and not just an excuse to have gratuitous sex with just anyone.