I'm assuming that you're talking about this to set up your group for the expansion. If this is not the case, please correct me. For old content you don't even need a dedicated anything anymore.

If you do new content that's challenging, you will need a dedicated healer. If this is ever not the case, I will want to quit playing. You used to need a dedicated healer in Kara - at least two even!

If the new content is well designed at all, you will quickly reach a point where having as much control as possible will be very important. Being able to choose exactly who to heal and when to heal them is important because there may be times when you need no healing, and hopefully some fights will be endurance fights. I think most multiboxers never reach far enough to see content like that, but that content is (or, was) in the game. And it still helps push progression even in normal content. You'll down things at a lower level of gear.

For me it's like playing a drum. You have three or four limbs each hitting their own drum at once, bass drum, hi-hat, snare, toms, etc. So I could keep HOTs going with my right hand while I tank with my left thumb while I DPS with my left ring finger. This is something anyone could do. I don't use a druid healer because I don't want to maintain a HOT stack, so I guess this factors into it.

I think it's great that you're running all those classes and I'm not trying to put you down. I swear I'm trying to offer my two cents to help you out. Good luck!