Counsel should always consider the merit of submitting a factum at the outset of trial.
In a recent, excellent text, Ontario Courtroom Procedure, 2007, Justice Donald S. Ferguson of the Ontario Superior Court of Justice, at p. 86 states:
"The Rules of Civil Procedure (R.R.O. 1990, Reg. 194) do not require factums at trial and it is not often that counsel provide them to a trial judge. But factums should be considered by counsel because the judge will better remember and understand counsel's position if it is left in writing rather than in the judge's notes. Ideally, a factum should be handed up at the outset of the case and then again, at the end, after being revised in accordance with any unexpected turns in the evidence."
It is my own experience, when I have assisted counsel at trial, that the submission of a factum at the outset of the trial is universally welcomed by trial judges. The factum can also serve as useful road map for counsel for the course of the trial, to be referred to prior to closing submissions, and to re-focus counsel following the inevitable diversions during the course of trial.