[lvalero]

It is probably not RAW but in my campaings any spell/power that is benefical and it is not resisted (or at least the rules don't show if it resisted or not) the target can choose to reject the spell/power. In that case she gains automatically the resistance roll and the spell/power has no effect.

Let's suppose you are going to be healed (as in "Healing" advantage) BUT you really hate the cleric or god that is going to heal you. Or you really really want to die. Then, if the healing power don't have a resistance roll, you automatically resist and the power fails.