Legacy quests are previous story quests, allowing you to be a part of the story that has already happened. While what your characters do in legacy quests do not count towards quests going forward, you can still redeem previous rewards and tell your kyvalorian's part in the story.
Learning new skills is important to any adventurer, especially if they can help you out on the field.
These quests will help you learn new crafting recipes. Some recipes are seasonal, and some have special requirements to learn!
Recipes learned are per account and not per character so you will only ever need to earn a recipe once.