I used to think the option was cool. But it just seems that they just make you weaker in a way or limit you. Now what I mean by that is that the transformations become totally useless in the higher difficulties. Sure the transformations are very cool but werewolf battle forms offer little protection when you're on master or legendary and it's just an easy way to get cut down. Vampire is good but none of your added bonuses help except for disease and poison perks that automatically come with it. That seems to be all it's good for. other than that in the higher levels you come to rely heavily on your skills alone. Whether you're a mage or a tank that uses enchanted weapons it seems the two don't offer much later down the road. So as of now. I never choose the option or I get cured after the Companions story line. Just doesn't seem to play out long term. If I don't need, I hock it.