The Quest Log basically tracks the progress of your active quests, and serve as an archive for your completed ones! If you’re ever stuck on some quest, consulting your Quest Log will probably help you out.
Example's Below:
When tracked, a shortened version of the objectives will be stickied to the top right corner of the screen, which helps a lot in these types of quests. (probably capable of tracking for crafting recipes as well), so you can keep a list of ingredients on screen while farming!
Example Below:
