No, soaking is optional. The main reason to soak grains is that it might make them easier to digest. Keep in mind that pre-soaking grains also shortens the cooking time by quite a bit. If you soak buckwheat, the cooking times listed here will be too long. To soak buckwheat, put it in a deep bowl covered by several inches of water. Let it soak at least 4 hours, but ideally overnight. Rinse the kernels after soaking.