Whole vs ground
Whole spices keep their flavour for years; ground spices start losing it within weeks.
Also: whole spice, ground spice, buying whole, pre-ground spice
A whole seed, bark or pod protects its volatile oils inside intact cells. Grinding breaks the cells and exposes oils to air, so aroma fades rapidly. Whole spices can last two to four years in good storage, and ground ones roughly six months before noticeably weakening. Cooks prefer to buy whole and grind in small batches, or to toast whole spices first. Some spices are more practical ground, such as turmeric and paprika, which are made from roots and fruits that are hard to grind at home. Whole spices also have different uses: they are placed in oil or in a pot to infuse, and removed. Ground ones disperse and thicken.