Given the currency of this topic it is worth reflecting on its relevance to superannuation.

Essentially the superannuation rights of a defacto partner (including same sex couples) are much the same as those joined by marriage. They are not identical though. The difference can be significant when applied to death benefits.

Couples joined by marriage hold indisputable proof of their position. Defacto couples may register their union in some jurisdictions but, essentially, a surviving partner may be called upon to prove that their relationship was not simply one of shared accommodation. A surviving partner may need to provide evidence about their living and childcare arrangements, sexual relationship, finances, ownership of property, commitment to a shared life and how they presented as a couple in public.

In the case of same sex couples, additional homophobic prejudices may enhance the possibility of a challenge by the deceased’s family members to any superannuation payouts to the survivor. Such potential actions, taken as a matter of principle, will support the adage that the legal profession generally emerge the winners of estate disputes.

A divorce will nullify a binding death benefit nomination. Whether or not a defacto separation is effective in nullifying a binding death benefit nomination will depend on whether the relationship has ceased to exist at law. This may need to be settled in court.

Essentially, in contrast to many defacto relationships, marriage brings certainty to both its inception and dissolution.

There are other, very important, considerations that have nothing to do with superannuation so have not been considered here however you may be interested in a comprehensive comparison, focussing specifically on same sex relationships, which has been prepared by the ABC fact check team.