Any plan needs a little tweaking while being implemented. A manager can never foresee every possibility that will impact an enterprise. Discoveries in technology, changes in the weather, advances in process and the whim of the consumer all change the way a farm plan can be enacted.
Farm plans need to be modified and updated to maximise profit as produce can fall in and out of favour and prices fluctuate. In response new business ventures may need to be explored and diversification or value adding may be required to boost profit. One particular family owned dairy farm switched to olive production just over a decade ago and now creates a range of value added products successfully selling directly to restaurants. The dairy farm simply wasn't as profitable or enjoyable for that matter.
New machinery, products or advances in process may become available and are too good not to invest wither money or time in. I spoke to a farmer who made the choice to invest in drone technology which gave the ability to take thermal readings to help manage irrigation on their land. While it wasn't in their original plan to take on such technology, the time it took to research the equipment and learn to operate it was well worth the adjustment to their overall business plan.
Fluctuations in pests and diseases, weed outbreaks and weather impact on how cycle in the farm plan is enacted. It may need to be adjusted to return a piece of land to a better state after unseen circumstances. One particular grower in the Virginia farmlands spoke of the effort placed into building their soil, adding nutrients, organic matter and micro-organisms to the top soil and how it was all washed away, literally, in the 2016 floods require major adjustments to their farm plan.
Employee skill level was also raised by one farm manager I spoke to. There were many "dreams" in his farm plan that he could not enact because he currently could not find workers with the required skill or initiative.
Any plan big or small should allow for adjustment. There will always be unforeseen variables that need to be monitored and reacted to. A farm plan should be flexible and organic.