I try to do this in our raids, personally, for a few reasons. It lets me determine the weakest links, for one thing. It allows all the healers to shine (if I do my job right and put them where they should be). It avoids the mana issues (seems to anyhow, but our healers outgear the content we run, we're a lol noob guild atm). "Snipe" healing is minimized (except me in my jerk atonement spec, of course). It feels more relaxed for us over all, lowering the triage feel. If (when) someone dies, we can quickly determine who was healing them, and see if it was a out of range of healer issue, an overwhelmed healer issue, or a derp standing in bad stuff issue. We have fewer instances of "well I was going to heal player A, but healed plyer B instead, and so did the other healer, so player A died".
I dunno, I guess I just miss the sub organization healers used to have. We were closer, then I think. Had our own /healersrule channels (ok, assignment/ dps are idiots channel, but sshhh), etc. :-(