In the Biodynamic Calendar timing is integral. To put it simply, when the moon is in different places in the sky, it has a slightly different effect. It is as if the Sun is the hour hand of the year's clock and the Moon is the minute hand. In the time that the Moon takes to move through all twelve signs ("hours") the Sun only moves one. This is a grand clock. You know that morning is different from evening. You do one kind of work in the morning and one kind in the evening. But there are certain things you do at 12:30pm, perhaps every single day.
If you imagine each "hour" of a clock as belonging to a specific zodiacal sign, you begin to have an image of how the calendar works through the year. Each "hour" has its own character, just as the mild morning light is different from harsh midday light or evening twilight. When the Sun (or Moon) passes into a different sign, the subtle light of the cosmic clock changes.
Should we be rigid about the calendar? Of course not. If you run a market garden (or simply have to eat!) you can't consider every imaginable factor. If you wait for the "ideal" time, you'll never act at all.
In fact, if you are really attuned to the influences of the cosmos, the alchemist Paracelsus says we should be able to replicate the effects of specific astronomical conditions ourselves:
"The skilful artist, however (how well I remember!), will be able by diligent consideration to prepare 'metals' so that, led by a true method of reasoning, he can promote the perfection of 'metallic' transformation more than do the courses of the twelve signs and seven planets. In such matters it is quite superfluous to watch these courses, as also their aspects, good or bad days or hours, the prosperous or unlucky condition of this or that planet, for these matters can do no good, and much less can they do harm in the art of natural Alchemy. If otherwise, and you have a feasible process, operate when you please. If, however, there be anything wanting in you or your mode of working, or your understanding, the planets and the stars of heaven will fail you in your work." - Paracelsus, The Hermetic and Alchemical Writings of Paracelsus, vol. 1, trans. A.E. Waite, pg. 16
Working with the Biodynamic calendar can improve yields and help support a more conscious approach to gardening, but if it becomes rigid or prevents common sense from being applied, it becomes a problem. As a practical farmer, we must first consider the geology, our climate, the weather patterns, and then the subtle effects beyond what our eyes can see. If we plow when the soil is completely saturated, we will just create a horrible mess even if we make such a mistake on the "ideal" calendar time. Common sense must prevail when it comes to using the planting calendar.