The healer is a class that is in the Miniatures Hanbook for 3.5 edition. It is a very focused class which may not be appealing to many players. Theybare not useful in melee combat as they are the only divine classcthat really cant wear armour or use shields. However they can be useful flr the following reasons: 

  1. In a war campaign with mass battles and large parties. This class is in the miniature book for that reason.
  2. A campaign that fights undead as cure spells hurt undead. 
  3. A campagin with a DM using creatures and villians whom how likes poisioning or cursing players
  4. A party that has a lot of strong melee players and no magic users who need healing. As the healer wont be needed to do much combat
  5. In a gestault camapign with another class that uses wisdom and does not wear armour (example: healer druid) 

There is always a way to use any class cleverly and be useful.