We believe in living the laws of the land, that means that while in the early church polygamy was practised it is no longer practiced and hasn't for over 100yr maybe even 150 yrs.
1 of the reasons, but not the only reason, it was practiced was that so many men died as a result of the persecutions that women and children were left with no means of protection or support. To the best of my knowledge men had to be interviewed by church leaders and had to prove they were living the gospel standards, had the means to support an additional family and that weren't doing only for carnal reasons