If a marriage includes multiple husbands and wives, it can be called a group marriage.
Wives', especially senior wives', status in the community can be increased by the addition of other wives, who add to the family's prosperity or are a sign of conspicuous consumption (much like a large house, domestic help, or expensive vacations would be in a western country).
For such reasons, senior wives sometimes work hard or contribute from their own resources to enable their husbands to accumulate the bride price for a second wife.
The wife's family, in other words, must provide a replacement for her thus maintaining the ties between them.
Both levirate and sororate may result in a man having multiple wives.
If every brother married separately and had children, family land would be split into unsustainable small plots.