Anyone who possesses a Crop Garden in their back yard would be wise to learn Croppery because anyone who knows Croppery will yield twice as much crop product from a plot (along with benefits to mood and imagination).
Advancing your Croppery skill to the second level means you'll use less energy planting, watering and harvesting your crops. And every so often, the land will give you a little super fun happy bonus present.
Croppery III makes you a veritable master of the garden, giving you more mood and imagination for tending your crops through their lifecycle, and yielding a higher chance of surprise bonuses (or bonus surprises). Above all of that, every so often you will have a 'super harvest', which yields double the amount of crops from a plot.