The primary purpose of a personal injury demand letter is to tell the recipient's insurance company of the costs of the damage they've caused in a favorable light for the injured party. Doing this may result in resolution and payment rather than litigation in many cases. However, it is also a clear part of the paper trail that you might bring to court if the party who has caused your injuries claims they weren't at fault, or the insurer otherwise feels the claim isn't valid. This document shows that the injured party (you) made a reasonable effort to seek reparations before filing a lawsuit.