(only a ...bad? healer can use an addon that makes choices for him)
I fail to see the difference between these two scenarios:
(1) Tank gets hit for 500
(2) I decide to heal him with Heal Rank 3 for ~600
(3) I cast Heal Rank 3 on him
OR
(1) Tank gets hit for 500
(2) I click-heal him
(3) SmartHeal decides to heal him with Heal Rank 3 for ~ 600
The difference being that I don't need to have a keybinding for every healing spell & rank, nor do I have to memorize their effective values combined with my +heal at that moment to maximize my mana efficiency.
And yes, before you counter-argue with "BUT ACTIVE HEALING VS REACTIVE HEALING", I already pointed out that it's entirely possible to force the addon to cast the max rank available. I honestly cannot see a situation where it would benefit the group / raid that I pre-cast Greater Heal rank 1 over Greater Heal rank 2. If you're pre-casting, you're already preparing for the worst case (tank getting crit) so you're not worrying about overhealing.
I'm sorry if I sound defensive but this shitting on a useful addon, that I would wager makes me do less overhealing and thus waste less mana and being a faster healer than people relying on their memory and dozen keybinds.
In any case, the point is kinda moot since it's not functioning with raid frames.
As for your comment about other players, it is entirely possible to heal raid-wide while selecting your target each time through raid frames. That's how I did my healing in vanilla and tbc raids.