In Oregon, there are certain statutes and conventions which funeral directors, hospitals, and others look to in determining who can make decisions concerning funerals and the disposition of a body after a person dies.
If there is any question about there being a dispute among family members, it can be very wise to create a document that gives the power to make these decisions to a specific person.
This is especially true if the person who you want to make these decisions is not actually your closest blood relative. Such a designation would overrule the normal list of people that is set out in Oregon law regarding to whom funeral directors and others would look for instructions in such matters.
It can also be very important to have a document setting out who should make such decisions if you expect two of your relatives to have different opinions on how your funeral should be handled, and/or what should be done with your body.