A healer is a must in almost all armys.

well, for the most part a healer should be included in most armys for two reasons: it allows your figures to have more staying power and allows you to push more without too much fear of reprocussions wich allows you to get more attacks in than your opponent. On the other hand you must "protect" the healer because in order to get the most out of healing, the healer has to be as close to the battle as possible (wounded figures dont move that quick).
Personally I do not use healers in most of my armies because I enjoy playing multi-dial figures and a lot of units with vamp. If i can fit a CP or leech medic in I will, I used to play a nice formation of blademistresses and a leech medic a lot.

yea i all way try to put in a head or do that dont need to be that good like 20 pts like a shaman

I always try to add in an EGM, Astrus, or something else to my armies in 300 points. Usually a **Crystal Protector is a staple in them as well, allowing me to heal with 2 figures, yet remain cost-effective. I think you have to weigh it on what type of build you are using. An all out melee army may not be able to heal as much, since they are always in base contact. A couple CPs could help them up the field, however, while adding healing. A hit and run tactic like GA armies NEED a healer, no matter what. In the skirmishes, your figures will both get hit, and push. Channelers or an EGM are perfect in this role, IMO.

With heavy defence, it becomes slightly less of a necessity, but stilll a necessity, just in case. Healing lets an army recover from mistakes. Mage Knight is all about mistakes. Whoever makes less mistakes wins. By negating some of your mistakes, you are increasing your chance of winning.

Just my opinion,
John

A healer is always a good idea. i find i like the solonvi channler the best. the stander version has that 12" range with 10 attack and 3 dmg. this lest it heals almost always hit a weakend char the range lets her stay somewhat out of the battle and still heal. she has a decent attak and dmg to defand herself and can take a couple pushed to heal if you need it. she is around 40 some odd points but i think the price is worth it almost every time.

Heh, healing is always good (until they fix Regen), but here's the more important question: Just how much influence does your healer need to have? Should it control the board and cause threats as well, or should it just be there to recharge mounteds?

Almost every army type should have at least one healer, but I think there's one exception: KI swarm

I've played with those dozens of time and my final conclusion is that a healer in that type of army is most of the time a waste of actions.
Bone toss should also doing nice without a healer.