I wrote about this concept in a recent forum, but I will repeat it here. In the world of education, there has been an evolution in the thinking of instructional content. A common descriptive term for the two kinds of learning being differentiated is "Just in Case" instruction vs. "Just in Time" instruction. "Just in Case" instruction piles information into a course that someone MIGHT need to know sometime in the future. Some of that is essential. In scuba, an example of good "just in case" instruction is the use of an alternate air source in case of an out of air emergency. The odds are that someone will never need that instruction, but in case they do, it comes up unawares, and the diver will need to know it when it happens.
In the case of less critical information, "just in time" instruction allows the learner to receive the instruction only when it is needed. A lot of divers will never do any underwater photography, so we don't clog their early training that information but rather let them seek out that training when they decide they need it. There is some dispute about what constitutes good topics for just in time instruction. For example, one frequent critic of the current diver education system frequently insists that all divers need to get detailed instruction on diving with tides and diving at altitude (more than what is already in the course) during open water training. Others point out that an overwhelming percentage of divers will never dive at altitude or in areas where tides make a difference, and neither event should sneak up upon them unawares, so it makes sense to wait until they need that information to teach it to them. Another frequent critic on ScubaBoard has argued that all OW students need to be taught how to tie a bowline with one hand while wearing a three fingered mitten, just in case they ever need to do that. Others argue that not many people will ever be in a situation where they might possibly need that skill, and when they realize such a dive is coming, that would be a good time to learn it.
When you look at the potential for scuba instruction today, the possibilities seem endless. There is far, far more that is possible to learn now than in the earliest days of instruction. Should we pack all of that into a mammoth and incredibly expensive open water course with so much extraneous information that students cannot retain the really important things they need to know, or should we teach them the essentials and then offer them a collection of additional courses from which they can pick and choose according to their needs?