Pre-arranging and pre-planning are in effect the same thing It means that an individual or a near relative (or someone who holds a power of attorney for an individual) organises their wishes prior to death. These wishes are written down and are photocopied so that individuals or lawyers have a copy themselves and the original is held with the funeral home.
This does not mean that everything is 'set in concrete' as individuals can change their minds, add different songs or poems to their wishes and update them as often as they wish. It does however mean that families are comforted by knowing what an individual wishes and means that a funeral can be personalised.
It also means that the information required by Births, Deaths & Marriages for the issuing of a Death Certificate is available immediately and means that families can grieve rather than spending time trying to find information which may be difficult to find such as the age at which a person was married.