What is the defence of insanity in criminal cases?

In Regina v. Smith (1968-69) 5 C.R. 162, the accused was charged with "four crimes of rape, two crimes of causing bodily harm with intent to wound, maim or disfigure; and with one crime of robbery." The trial was by judge and jury. The defence was that of insanity. The learned trial judge, after charging the jury requested comments from counsel. Counsel for the accused made this submission: "One other matter, I also felt in cases where insanity is the defence, and particularly in a case like this where the facts are rather horrendous, when the jury are told that their verdict is not guilty by reason of insanity, they will labour under the completely mistaken apprehension that that means the accused will be leaving the courtroom with all of us this afternoon. Do you not feel that since it is mandatory, just as say a sentence of death is mandatory in a capital case, or a sentence of life imprisonment is mandatory in a non-capital case, where it is mandatory--that he be detained during the pleasure of the Lieutenant-Governor--"