CC stands for Crowd Control - anything that roots, stuns, ectectect is considered CC. Very useful in PvP or when dealing with multiple enemies in PvE.
Here are some of my favorite skills for my nightblade healer:
Funnel Health - a DoT (damage over time) spell that causes a HoT (heal over time) effect on me AND another ally. A heal that also damages? Yes please.
Crippling Grasp - I hurt you, I imobilize you, AND I steal all your speed. Super useful for a squishy healer in robes! By the time you realize what's happening I've already gotten away!
Sap Essence - An AoE (area of effect) spell that boosts my weapon damage (on resto staff, this means it boosts my heals) AND heals my allies for every enemy I hit with it.
Dark Cloak - I go freaking INVISIBLE and can drop FOUR DoTs that are on me. Again, squishy healer - so useful! A healer that can disappear in PvP is going to be amazing.
Shadow Image - Excuse me while I summon this shadow from the underworld that lowers boss damage by 15%. That is 15% damage that I don't have to heal!
Reaper's Mark - In a dungeon and we're fighting a big group of trash mobs and I'm low on health? Let me just mark you so I can ignore 75% of your armor and when you die I get SIXTY percent of my health back, thanks.
Focused Attacks - Hitting with the heavy attack of the Resto staff heals my group and returns magicka to me, and this little buff gives me an extra 30% weapon attack speed so I can do it faster. Oh and hey let me just get my stamina back so I can dodge everything and never get hit, that'd be nice.
Those are just a FEW of the NB abilities, and I haven't even mentioned passives - the one that give you 20% boost to potions (TWENTY PERCENT BOOST TO MANA POTIONS YES PLEASE I'LL JUST BE OVER HERE CASTING *ALL* THE SPELLS), the one that gives you magicka when you kill someone with an assassination spell (Did I mention I can cast -all- the spells with my stupid amounts of mana?), the one that gives my extra ultimate when I hurt someone with a siphoning skill (Guess what my ultimate does : lots of damage, lots of heals - notice a pattern?).
I honestly don't know if nightblade is going to be the "best" healer. But goshdarn they are definitely the most fun, at least to me