Q: Who is CC for?

A: Everyone

Wrong!  Okay, it is right but it is also wrong.

Lets see how it helps the tank.
Plus:
1) Single target threat is so much easier.
2) One/Two mob(s), 3-5 seconds alive means no need to ever use cool downs.
3) Most servers do Skull first and X second so there is no explaining needed to keep people on the same target.
Minus:
1) Positioning takes more work so you do not break it.
2) It takes more time to assign CC and mark.
3) You have to pay attention to anything that might hit more then one target.

So it helps the tank and it hurts the tank.

Lets see how it helps the DPS.
Plus:
1) Lets face it, single target DPS is all that really matters.
2) You can prove you know what your doing if you are good at CC.
3) Less mobs means less chance of getting hit and that means lower repair bills.
Minus:
1) No huge AoE numbers to inflate your ego.
2) You might actually have to have more things keybound to remember.
3) You have to pay attention to anything that might hit more then one target.

So it helps the DPS and it hurts the DPS.

Lets see how it helps the healer.
Plus:
1) Less mobs on the tank means less damage and an easier to heal tank.
2) Single target means it is less likely DPS will pull aggro and need heals.
3) Smaller pulls means less need for expensive heals and less chance of having mana issues.
4) Less time spent drinking.
5) Less chance to need cool downs.
6) Possible chance to do some DPS as well for fun. (Smite healing rocks)
7) Money saved from not having to have 40+ waters for every run.
Minus:
1) ...

CC is for the healer.  That is the concept behind CC.

So the real answer is

A: For the healer.

From the perspective of a Hunter I personally like having a happy healer.  A happy healer means that I will always get heals when I need them and I never have to look to using a pot or a bandage and that means I get more DPS time in.  I like a happy healer.

Bonus points for any Hunter that leaves a trap at the healers feet at all times.  They might never say anything but the ones that notice it and understand what you are doing will love you forever.  Sadly some healers have no clue why you do that.  It just means they are stupid.  Lets hope they can at least heal even if they can not understand precautionary CC.