My sisters are all amazing. One of them is researching polygamy and has written this series of articles. It presents an explanation of Joseph Smith's practice of polygamy. Here's the readers digest version.
The Lord commanded Joseph Smith to reveal that marriage between man and woman were eternal. It didn't matter if one spouse died. The other could re-marry and have their new spouse also sealed to them. This was an important doctrine because death and polygamy were/are common world wide.
Emma didn't want Joseph to be intimate with other women. Joseph loved Emma very much. So he didn't enter into polygamy after being visited several times by and angel and being commanded to enter polygamy.
Joseph is visited by an angel with a sword and commanded to enter into polygamy or die. This coincides with the discovery that John C. Bennett, a convert who is a doctor still married to a wife back east, has created a sex ring. He's teaching men and women that if nobody knows about the sex, it's not wrong.
So Joseph marries women who are either victims of John C. Bennett, or women who can help track down and testify against the predators. Being married to them, Joseph can interview them alone as well as provide for the victims. Eliza R. Snow is one of the victims of John C. Bennett that is sealed to Joseph.
But, according to my sister, Joseph does not have sex with his new wives. Some comments made by these women later can be taken as evidence for or against that. Imagine if you thought you were getting married and it turned out that you weren't going to have "relations" with your husband. That would be sort of a shock. And by the way, you can't go marry someone else.
One of the evidences my sister uses for this is our own ancestor Elvira who had children after Joseph Smith's death. But the dna evidence has not shown any children of Joseph Smith's wives, but Emma, to be his. It's interesting.
My sister has found that a lot of the people who were most vocal about Joseph Smith being a scoundrel were themselves part of John C. Bennet's group. Lovely. And typical.