Harvest down leaves the crop on the ground, harvest and pick puts the crop into your inventory. So using harvest and pick is quicker!
Originally the game left harvested crops on the ground. It was changed recently to give the option to put them directly into the inventory, as farmers were complaining of massive RSI!EDIT: If you want an easy introduction to the game, you may want to look at my "Guide for the aspiring hunter" in the Guides & Tutorials forum here:https://www.unrealworld.fi/forums/index.php?topic=6814.0It's a bit powergamey I know, but it will teach most of the game and give you confidence to try a harder start the next time!
Harvest down was left in place so existing method wasn’t removed. And sometimes it’s beneficial to harvest, then thresh on the spot. (Wild harvest such as meadsweet can get heavy as whole plants.)