The idea that there are 4 seasons seemed, in my eyes, to be as natural as can be. Every since I was a small child, the four seasons have appeared across cultures and on every calnedar I've ever looked at. It helps us process the state of the world that we live in and gives us an idea of what the natural world will throw at us in the near future.
However, a simple shift in perspective made me realize how aribtrary this is. There are infinitely many levels of granularity with which we could divide the year. Although, some of them do seem more practical and useful than others. We could go so far as call each day it's own season or even each second of the year its own season, yet there is little usefulness of this because there are far too many of these to process and there would be far too much variability year by year.
In some sense, having four seasons does seem natural, so there likely is some inherent truth to why many cultures use four seasons. The four seasons could be thought of in terms of weather as 1) Warming - Spring 2) Warmth - Summer 3) Cooling - Autumn 4) Cold - Winter. In this way, the four seasons denote the two states of warmth and cold and the transitions between them. This is one advantage of the simple system with four seasons.
With many more seasons, like the Japanese ko and sekki, different advantages and disadvantages are at play. The general trend of the weather of the seasons is largely lost because at a smaller scale, variability plays a much larger role. It is simply much less reliable to generalize the weather of a 5-day microseason year by year than it is to generalize a 3-month season where variability has less of an effect on the overall perception of climate. Nonetheless, there are certain events that occur more regularly at more precise times. In my research, I found that many flowers, such as cherry, peach, and plum blossoms, bloom at fairly regular times of the year. To say that a particular flower blooms in spring or summer seems like an oversimplification because it can be such an acute event. There are also certain flowers that bloom in the winter that are often overlooked because winter is seen as the season where many plants die. With more attention to finer time periods, those flowers, like camellias, get their respective attention.
In a broader sense, having 72 microseasons may be more inaccurate in a given year due to variable weather patterns, but that is likely not the only purpose or benefit of microseasons. Looking at the year in a more micro level can change our temporal perspective and bring us closer to the present. For instance, if I tend to only think about the current season, I will focus on events that could happen 2-3 months from now on a 4-season calendar, but when I focus on a microseason calendar I would only think as far as 5 days into the future. This allows us to enjoy the present is a bit more and stay a bit closer to it, when in world we live in tempts us to think too far in advance.