I think the question suggests further study. There does seem to be an element of arbitrariness, albeit a bright line, between when a prelim will be available and when it won't. There are a lot of offences that might require a prelim where it will be lost. Arguably, there are some cases for which a prelim might not be as valuable. I think further study on when a prelim is effective, in all aspects and in terms of learning about the Crown's case and screening out weak cases, would be useful. We can draw that line as to when a prelim is required and when it isn't.
On September 18th, 2018. See this statement in context.