When considering entering a civil partnership, if one or both parties has significant wealth built up via a business or inherited, then they may wish to seek to protect this in the event of the partnership failing. This can be done via a pre-partnership agreement.
When a relationship breaks down, a civil partnership must be formally ‘dissolved’ by the court which has powers to make orders relating to financial matters and any children, as in a divorce.
If you have a will, you will need to make another will as it will be invalid once you have entered into partnership and any trusts will need revising.
Same sex couples who want children should seek advice from a family lawyer as the situation can be very complicated and several legal issues can arise regarding parental responsibility.