If you are doing dungeons you probably have a healer so your self-heal should not be expected there. If you are doing group quests with a group the same should apply. If you try to solo group quests it is a good idea to have a tank specc. At least in WotLK one could solo nearly every quest without any problem as a tank. That could just be your second specc for the big ones.
I do not know how the quests will look like in Cata. Since now they seldem implemented big quests without pre quests that needed some grinding. So I doubt that we will be able to level well without grinding (dungeons will help there like they did in WotLK).
Anyway, I think that all the healing stuff is best for grinding. It can drastically reduce your down time to heal your self up with food or bandages. In most cases you do not die while questing. You just wear your health down so that you need some break. Your self healing capabilities can help you there.
Tanks do not have that problem, they normally can ignore their health bar while leveling. They do not have such downtimes. But their dmg is lower so that they kill stuff slower.