It's somewhat useful to quickly regain your mana if you were in human form, although it only works where you have space. Eventually though, with enough points into Intelligence, your mana regenerates faster than you can deplete it even in human form.
The Dragon healing spell is usually enough, but you can supplement it with potions (which do work in Dragon form). The Dragon's primary form of defense is its mobility, and it's only in one or two spots where you can't evade well (Zagan) that are dangerous to the Dragon.