I honestly do not understand the finer points of it, but... I do not descriminate against anyone for their choice of lifestyle. However, as I am the only person posting thus far, here are some interesting ideas for why one might choose polygamy as their means of finding some enjoyment in relationships. If you have more information or a deeper view, please by all means, add to this.
polygamy has strong roots in the morman and christian and wiccan and other faiths
Perhaps you are christian and love one or more people in a romantic, sexual, fiscal, or otherwise manor... or are really bored with your spouse... or just like legalities and ownership and contracts and have multiple love interests...
polygamy is for you! a simple, moral, legal solution... well, the legality is questionable... since rochester is in america and polygamy is illegal in america... blame perpetual union of church and state for that one...
polygamy \Po*lyg"a*my\, n. [Gr. ?; cf. F. polygamie.]
1. The having of a plurality of wives or husbands at the same time; usually, the marriage of a man to more than one woman, or the practice of having several wives, at the same time; -- opposed to monogamy; as, the nations of the East practiced polygamy.
2. The condition or practice of having more than one spouse at one time. Also called plural marriage.
3. Zoology. A mating pattern in which a single individual mates with more than one individual of the opposite sex.
See the Note under Bigamy, and cf. Polyandry.