Some definite pluses and minuses appear in works such as The 19th Wife, depicting in detail the lives of wives and children past and present within Mormon-style plural marriages.
Some women welcomed the relief of sharing household and marital duties with sister-wives. But as a man accrued wives, some would be shunted aside or consigned to a lonely retirement as the new favorite took her place.
The men seemed to enjoy the benefits much more than the women, at least as shown in this and other books on the subject; but in a paternalistic society, that’s scarcely a surprise. However, the men did have to provide housing and sustenance to their swollen households, or several separate households, and that came more easily to some than to others.
To some, plural marriage is, or was, a religious duty, according to their beliefs. Men were expected to take a second (or other) wife whether they wanted to or not, in order to fulfill the precepts of their religion.
The case you cite may not have anything to do with religion; but you posed a general question about the benefits, and I don’t think many in our culture know more about that than the Mormons.