This is a quality of life mod which provides a number of extra tools and information for your grow zones.
Q. How does smart sow do its prediction exactly?
A. It fetches the grow zone's plant's def and calculates how many ticks it has left to grow. Then it internally simulates its growth over that duration and forecasts the weather along each step. If the plant is predicted to survive to its minimum harvest day, sowing is allowing.
Q. How does food estimation work?
A. All pawns and prisoners in the colony (does not include away pawns) have their hunger rate (nutrition eaten per day) cached periodically. This factors everything from race stats, implant buffs, traits, etc. Added all together, this value is compared with the estimated zone yield if it were processed into meals (you can configure this in the options).
Q. Performance impact?
A. Most of the code just runs 1 tick out of every 2500 (hourly) to update the cache. The rest involves the workscanner and has a negligible impact as it just uses that cache data.
Q. Zone priority is not working for harvest?
A. It is, but it can be misleading. When a job package is assigned to them, it includes multiple plants. If there was not enough plants in one priority to fill their package, they'll include some from the next priority down. They then work on their job package, starting with the closest plant.
Q. What about grow zones within indoor greenhouses?
A. Most of the functionality of this mod skips any plants that have a roof over it.