For the same reason that draft requests to charge should be prepared in advance, a draft summation should be prepared as an outline of where you expect to be at the conclusion of the case. Of course, the draft summation, in that form, will not be utilized. In fact, its real purpose is to suggest what your case should look like in its most favorable light, assuming all the evidence goes in as anticipated. From this draft closing statement, an opening statement can be prepared. An opening statement is the last thing that should be prepared before the trial begins.
Some experts say that the opening statement is the most important part of the trial.
While this may be disputed, a good summation utilizes the opening statement of both sides. An opening statement provides the opportunity to identify and tell the trier of fact what the case is about. The theme selected will stay with the case and be in the back of the jurors' minds throughout the trial. Never promise more than you can deliver in an opening statement because the jurors know intuitively that what you tell them you will prove, and must prove. Likewise, from the plaintiff's perspective, it is wise to anticipate the defendant's theme and to try and create a question or doubt in the mind of the jury before the defendant ever introduces his theme.