Usually, people don't engage in relationships with multiple knowing partners for pure sexual satisfaction.
I had a TA last semester from Tibet who talked about the three different poly's and he spoke about doing research in a farming community where polyandry and to some extent, polyamory, was normal. It was due to the fact that when a family has children, that means the land will have to be split up between the children when they grow older.
If a woman has two husbands and a few kids, then the land won't be divided up as much as it would be if both husbands had individual wives. Sometimes, polyamorous relationships will arise when a woman or man is sterile or couples or singles will see the benefits of raising children and working together along with having the foresight of how those children may care for them in the future.
I suppose to the pure sexual side of your original question, how a man in a polygamous relationship has sex with ten wives at the same time, he probably doesn't. That's alot of loving to go around and for a man to do that, he better have the endurance necessary and the finances needed to care for so many. It's safe to say very few men in history have had more than a couple of wives.
In Saudi Arabia, I believe men have to be able to care for each wife equally. I think men are supposed to have seperate houses for their wives. Kinda like having an affair that everyone knows about. | 
