Yarrow has so many medicinal and garden uses too many to list. If I use this herb for one thing than these are nasty deep cuts (secateur). A must for a gardener and woodworkers!
Cooking:
Yarrow has a bitter taste. You can add the leaves to salads and omelettes; sparingly so as not to over power the dish. Yarrow also makes an interesting addition to chicken soups and stews. Yarrow flowers make a wonderful aromatic wine.
Growing:
Yarrow is easy to grow, likes full sun, neglect and a dry spot. There are a lot of ‘improved’ cultivars for the ornamental garden, my guess is, that they might cross with your medicinal yarrow and lessen the effectiveness.