So you want to keep healing the fully healed tank because you have them in your focus orb? Or even through that last heal scroll on the tank with 1HP short of their max?
I like the "hold down the key" method of healing, but I think autoattack is asking for it.
And maybe its just me, but sometimes I quickly tab to the bad guy during a log fight since knowing where they are helps me judge how I should be approaching the battle (or in the case of something like the Tor dragons/giants lets me help coordinate the battle). Doing that with autoattack on would mean I'd end up tossing scrolls on myself during those few seconds.