Unless a person already has soluble fiber or prebiotics in their diet, I always recommend them. Fiber is the #1 nutrient lacking in the American diet. Soluble fiber is useful for constipation (although non-soluble fiber is even better for this), it also helps inhibit post-prandial blood sugar rise (so for people with T2D or MetS), lowers unhealthy blood lipids, promote healthy gut flora (people with gut dysbiosis, leaky gut, IBS, etc).