it would be best to have the option to toggle at any time. I would like to use it when building, planting, felling, digging, hoeing, placing objects. And I also agree with displaying the current amount of fertilizer and possibly changing it depending on the fertilizer used.
Us that do a lot of infrastructure work (roads, district mapping, etc) would love a toggle to show the chunk lines.
even better: show the plot, the nitrogen/phosphorus/potassium levels of the current plot in a tooltip, and the amount change based on what fertilizer is in hand if added.
Heck, that'd be useful to not just fertilizing but for building purposes too! I wouldn't mind having a survey equipment for just that purpose. The claim tool is useless outside the circle of influence these days!
This was implemented in Update 13.