Help with macros?

[Itseotle]

I suppose 0.016 seconds is correct. More precisely read time depends on frame rates; 33.3ms/line in 30fps or 16.7ms/line in 60fps.

Sounds about right, so if you have 1 macro line for the icon, one for the call out, one for the error off (cuz who likes error spam?) that leaves you 12 lines for the action itself. 12 x (1/60) = 0.2 or 200 milliseconds, is a MUCH bigger window of time than it may seem to execute your macro and still have it fire even if your GCD is not ready. I personally have used both single line actions and multi-line and the multi-line is by far more reliable in most* situations.

*some times you do not want to use this though is abilities that toggle with no cooldown (Defiance/Cleric Stance), macros that use multiple different abilities per macro, and certain pet commands. As a side note, using this with ground target AoE produces a very cool trailing effect.

[Itseotle]

Nothing really comes to mind that needs macros.

I would argue that any buff with a cooldown that is casted on someone else, involves three or more people, and isn't part of a rotation would be called out so that the group can make the most of the buff or coordinate buffs. Examples you didn't mention are things like :
eye for an eye
Goad
Apoctostasis
Virus
Mantra
Living dead/hallowed ground/holmgang
and to a lesser extent, silences