For me, I have a series of buttons depending on the situation. I run 5 classes on 1 comp with keyclone.
I run Pal, Warlock, Mage, Priest, Shaman and pretty much instance whore.


I have a "Nuke" button. This maps to everyone but the Pal and their own castsequence of nuking. Though the mage just hurls fireballs.

Then I have a 'Nuke sans priest' button, which is the same as above but leaves me priest available for healing when I anticipate that the 2.5s, or whatever the cast for smite is, is too long.

I then have a "heal paladin" button for the priest as well as the shaman, which I rarely use other than "all hands on deck heal".

With my particular setup, I rarely need to heal people other than my Paladin.



Part of multiboxing, as I'm finding out, is to reduce micro as much as possible. By doing all this bundling, I do end up lowering my efficiency, but when situations demand I get in there and go micro crazy I retain some efficieny with a single nuke and single heal button. If you can manage the micro of all the button clicks that real granularity demands, then go for it I guess.