It can protect either or both of you in the event of a relationship breakdown. It can operate in a similar way to a prenuptial agreement by making it clear how the pre-owned assets of one partner are to be shared with the other if you should break up in the future or if the property is owned in the sole name of one party and another party moves in. It can make it clear for both partners that contributions towards utility bills by one partner may not entitle them to a share of the property itself if you should break up.