You need to be careful with something like that.
It needs to hold to the rule of one action from the user does no more then one keypress or mouse-click in game could accomplish.

One click = one action per client.... if fine.
If you could click once and have it do multiple things that could not be done in game... that's not fine.

Take the G11/G15
A macro which casts Elemental Mastery (no GCD) followed by Nature's Swiftness (no GCD) followed by a single Chain Lighting (incurs a GCD) can be accomplished in game with a single mouse-click or keypress of the associated macro.
So making a G-macro which does all of these on one click is fine.
Making a cast sequence which will, "Curse of the Elements, Corruption, Immolate, Shadow Bolt, Shadow Bolt, Shadow Bolt" is ok, if it requires one click, one keypress or one G-press per action.
Using the G-macro to insert delays and press 6 times in sequence on your one click is not ok.

I've gone into the warcraft keybinds and given my thumb buttons (Firefox/Explorer default page forward, page backward) keybinds, and then placed in-game macro's in those slots.
The use of the mouse for in-game actions is fine, as long as it does no more then could be done with in-game abilities.
Any software that provides potential for more then this should be evaulated carefully, and definitely never used for additional functionality then can be achieved in game without it.