Is the concept of, "good faith" in English Commercial Law an adavantage or a disadvantage?

The principle of good faith in English law can be traced to the early case of Carter v Boehm (1766) 3 Burr 1905 where Lord Mansfield first formulated it. According to his lordship, "good faith forbids either party by concealing what he privately knows, to draw the other into a bargain, from his ignorance of the facts, and his believing the contrary". Its general origin is known to be found in equity as oposed to common law given the fact that equity was widely known for its promulgation fairness and justice. Subsequently, Parliament introduced and gave a definition for it in section 61(3) of the Sales of Goods Act 1979 (see link http://www.statutelaw.gov.uk/content.aspx?activeTextDocId=1837068). However, despite this introduction, its reception has not been without mixed feelings; with the principal matter of contention being its ambiguous nature. It is feared that the interpretation of the equitable principle would lead to uncertainty in commercial contracts as it leaves a wide scope of discretion to the judges. Emphasis is placed on the fact that "good faith" is subjective in nature in dealing with the behaviour of the parties and therefore will be dependent on the peculiarity of each case and the judge's construal of it. Hence, this would uncertainty in the already structured system of precedence in English courts. Well-known commercial law judges such as Lord Browne-Wilkinson and Lord Millett have advised against the use of equitable maxims that hinder certainty in the law (see the case of Westdeutsche v Islington London Borough Council [1996] 1 AC 996 and Equity's Place in the Law of Commerce (1998) 114 Law Quarterly Review 214). This reasoning not only has theoretical but practical benefits as it would be time and cost effective for businessmen due to the fact that both parties will be able to envisage the outcome of their respective situations by examining past decisions in similar contentions. Even with the advent of a statutory definition, there is still room for uncertainty as the act still utilizes the subjective word of "honestly". What amounts to an honest act is undoubtedly a moot point. Overall, "good faith" seems to be creating more problems than the fairness it was set up to achieve.