There are several ways that these differ. For example, the flavor of all three will vary. Raw walnuts will yield the most bitter results; roasted have a more developed, slightly sweeter nutter flavor. Meanwhile, soaked and then either dehydrated or roasted walnuts will be the least bitter. Aside from taste, there are health differences. The roasted nuts will contain less overall nutritional benefits as some are destroyed in the heating process, unlike the raw nuts (or soaked and dehydrated). Going one step further, soaking nuts improves the bio-availability of the nutrients in the nuts, helps to reduce bloat/gas issues, and tastes less bitter. The only issue is the extra effort it takes to soak and dry the nuts.