Without a marital agreement, spouses generally fall under participation in acquired property. Income obtained during marriage, except gifts and inheritances, is generally divided equally on divorce. The other regimes are separation and community of property. Separation involves no division: each retains their assets. Community consists of each spouse's individual property plus common property that generally can be disposed of only jointly. Community and separation generally require a marital agreement or court order. For example, a court may order separation on a spouse's application because the other is permanently incapable of judgement or over-indebted.
Many do not know a property regime can change during marriage. A notarised marital agreement suffices. It may provide for the change retroactively from marriage or simply for the future.
Switching to separation of property until divorce makes sense, for example, if a long separation is expected before divorce becomes final. It prevents assets accumulated during separation from also being shared. However, separation of property does not affect pension sharing: second-pillar assets must still be shared for that period.
In short: If a long separation is expected and you do not want income earned during it shared, switching to separation of property makes sense. Both spouses must consent, however, and the financially weaker spouse often does not want to.