Purpose of written legal argument

Chief Mountain v. Canada (A.G.), 2012 BCCA 69 deals with an application to submit a lengthy factum (written legal argument).  In giving judgment the British Columbia Court of Appeal explained the purpose of written legal argument:

 

[10]         The main purpose of the factum is to provide the court and the opposing party with an outline of the arguments that will be advanced, and a list of the authorities to be cited. The factum need not set out every nuance of the argument, nor need it comprehensively quote passages of relevant cases. Counsel should be aware, as well, that the members of the division hearing the case will have read, in addition to the factums, the judgment or judgments appealed from, as well as portions of other filed material. The factum should certainly refer to that material, but need not be repetitive of it.