Here's another example: In Edmonds v. St. Francis Medical Center, Appellate Division, A-7109-03T5, May 20, 2005 the appellate court affirmed the lower court dismissal of the plaintiff's medical malpractice complaint for failure to provide an affidavit of merit. The plaintiff, whose counsel decided that a medical expert was not needed, had treatment for his toe, which became infected and led to gangrene, and then amputation. The trial court correctly dismissed the complaint because the plaintiff's claim involved issues that were not within the common knowledge of laypersons, including the proper standard of care for treating his particular condition and whether a deviation from the standard of care was a proximate cause of the loss of his toe.
Even in what is seemingly a res ipsa loquitor case such as a retained lap sponge after abdominal surgery medical expert testimony is necessary. If cost is a major issue, such as when a case does not have significant monetary value, then often it is possible to have one expert testify on all components of the case, standard of care, causation, and damages, where normally you would have three separate experts.