Yield increases and speed are significant leading to only needing one high level plant gatherer or grower to feed and water an entire fortress, also leading to much larger prepared food stacks (from syrup and bushes made at the threshers) and booze stacks. Not that they're totally awful at low level but having one person who is very good at growing is high priority in my embark.
I know about that and my embark team usually have 2 proficient growers. But it's somewhat in my mindset:
1. All dwarves harvest, all dwarves plant seeds.
2. Have a lot of individual farm plots (1x1 - 2x2 - 3x3) for many different crops.
3. Produce wide range of different drinks, but in small quantities. I try to keep every drink at around 50 units.
4. In long run around 50% of total population have farming enabled. Kids, military and important dwarves (medical, military, bookkeeper, manager, don't do that stuff.
5. This makes planting seeds faster during season change. 30+ dwarves do it much faster then 2, no matter skill difference. Even if I have best designed seed stockpiles, hauling every single seed adds a lot to total planting time.
6. 30+ planters do the job simultaneously. When harvest time comes, most plants are ready withing 1-2 days. This reduces hauling time for gathering crops. If there are a lot of plants, peon will come with barrel and take a lot of plants at once. If harvest period is longer (weeks) the same job (take barrel from plants stockpile, come to field, take one plant, haul barrel back to plant stockpile, hey-look! there is new plant on the field) have to be repeated many times. Not to manition, that plant will wither if not gathered soon enough. You can really get unlucky, if you legendary farmer hit get booze->break->sleep->eat->attend party combo.
Maybe it's not the best farming design, but I kinda like it. in 34.11 I played with seasonal crops mod, which required a lot farming space (2-3 farming plot squares per dwarf, and sometimes I still had to import plants or booze). In vanilia legendary farmer can feed entire fortress using 3x3 plump helmet farm.
Anyway, one of my megaprojects was "all dwarves legendary", where my goal was to make sure that every single dwarf will be legendary with their best migration skill. It failed on medical skills and some bugged ones (animal care, glazing) but at the same time 50 war grizzly bears were pretty awesome. To free animal hard-cap I periodically sent them to clear caverns from Forgotten Beasts.
You can count it as "proactive-reactive" design.