It's a nutritional substitute, not a cooking/baking substitute. Have you ever tried making scrambled eggs using flax instead of eggs? Ok then...
After having tried it, I would agree with you that it's only a nutritional substitute. But some people say, and it has been written (here on RJ in fact
), that it can be used as a substitute for eggs in cooking and baking.
From RJ: "...if you’re mixing up a batch of weekend pancakes, and find yourself out of eggs, you can use ground flax meal (one tablespoon plus three tablespoons water per egg) instead, since it can be used as a replacer in baked goods"