I've noticed lately that when I do endurance runs (even though they are relatively short), it feels more like "work" than other forms of running. When I do sprinting, I can feel the benefits shortly thereafter. When I run at VO2max pace, I can feel benefits shortly thereafter. But when I do strictly endurance work, I don't really feel much benefit, and it just feels like I've expended effort and not much else.
I think endurance is a component of total fitness, but it's relatively low in the ranks. Once a person can run a few miles or so, I believe the majority of health benefits are obtained.
Stretching endurance further and further out, as in a marathon, doesn't add much to fitness. Conversely, if a person can keep increasing their speed over a short distance, this will add a significant amount to fitness.
Eventually, I will see how little I can do of pure endurance work while still maintaining that component. Part of the difficulty I think is that endurance has a skill component, so if you do it infrequently, you may not lose your aerobic fitness, but your skill level may suffer.
I will experiment and see what kind of frequency is ultimately needed,
