What is the effect of requiring an undertaking as to damages under an interlocutory injunction?

I have reviewed Lord Diplock’s reasons in Cyanamid and I should note that on pp. 407-408 he states: One of the reasons for the introduction of the practice of requiring an undertaking as to damages upon the grant of an interlocutory injunction was that “it aided the court in doing that which was its great object, viz. abstaining from expressing any opinion upon the merits of the case until hearing”: Wakefield v. Duke of Buccleugh (1865) 12 L.T. 628, 629. So unless the material available to the court at the hearing of the application for an interlocutory injunction fails to disclose that the plaintiff has any real prospect of succeeding in his claim for a permanent injunction at the trial, the court should go on to consider whether the balance of convenience lies in favour of granting or refusing the interlocutory relief that is sought.