A dedicated healer, ie Resto Druid/Shaman or Holy Priest/Paladin receives the extra decurse on a friendly target, which the DPS specs do not get.

Not sure how important the removal of magical effects (Resto Druid, Resto Shaman and Holy Pally) or poison (Holy Priest) will be, and if you'll miss this ability without the dedicated healer type.

My PvE team has been: 1x Prot. Pally, 1x Demo. Warlock, 3x Elem. Shaman. While three shammies has not had an issues healing all 5-man content to date, they will miss out on a decurse effect which a resto would not.