People talk about pre-moving all the time, like it's something that is always possible, and people say that lag isn't too much of an issue. Healers are a class that often cannot pre-move because someone needs heals NOW, especially in Titan HM 'cos someone didn't dodge a plume, or the tank took a critical mountain buster to the face. As a healer, you know the next plume, bomb, landslide is coming, but you also know that if you don't heal NOW, someone's gonna die and likely cause a team wipe. So you take the gamble, start casting a heal, and hope it gets off in time. Of course, throw lag on top of that, and you're probably starting to cast a full second after you really should be as far as the server is concerned, and THEN a plume appears under your feet just as your cast is ending. You react and run immediately, sometimes the heal goes off, sometimes it doesn't. You're standing outside of the plume, start casting the heal again, it's half-way done, and BAM, you get hit by the WoL, and your heal is interrupted.
That's my experience, with international lag, trying to heal through Titan HM. I've tanked it, I've DPS'd it, and those jobs are SO MUCH easier to do it on such that I'm convinced that most every one who says "it's easy if you memorise and pre-dodge it all" never ever had to heal through it with lag.
