It's pretty much just the delay between actions, you will almost never get it as fast as the client-side queue, it's a bit like dark souls ability queueing, it's not as simple as mashing it 9000x a second, that can get you closer pseudo-queueing, I use one for flaming arrow on bard, but you will notice it if you macro say, ninjutsu keys, the fast smooth flow is suddenly staggered, again, you can do it that way, the client is just already designed for it

So long as it's not causing wipes, really not that bad, but just be aware of the limitations macros can have, at times they save me time (Eye for an Eye on T and TT, Virus too) but when I heal I generally want that heal to hit a specific time, if not as soon as possible, galvanize has this nasty delay to it too, the sooner it's on the better (Most of the time)

Again, just be aware of the limitations, they can both help and hurt, there's a good reason why it's GENERALLY frowned upon, it's probably overblown a bit, just the next time someone dies (For whatever reason, goofing mechanics, etc) examine your play, see if that heal hitting a LITTLE earlier would've saved them, the biggest decisions you make often will go unnoticed or happen in a split second, if clicking them was really that deciding factor or not