Theoretically, there could be 2 benefits to it:
1. would solve the problem of there being more girls than boys of dating age.
2. would solve the problem of the working mother- one wife would work to help support the family (as a second income, or so husband can learn) and the other wife can raise the kids.
But…it would never happen.
Aside from the fact that it is illegal, the practice does not just depend on the man-and what woman would want to become someone’s second wife? Singles are reluctant to do so even now when the first wife is deceased or divorced, can’t imagine they would want to when she is still in the same house! And what wife would want to share her husband with a “tzara”?