Please stop using macros to mark the enemy you are attacking

[GayRobot]

I don't care, as long as you don't use the macros to make a countdown.
The marker on someone going 5, 4, 3, 2, 1 by the second is completely unhelpful.

This is used to coordinate a surprise target switch, so that the target being bursted doesn't recognize they're in danger until it's too late—preventing them from pulling away or using defensive cooldowns.

This way of coordinating burst was important enough to Feast that Square added the "Focus Attack" quick-chat to replace marker macros (and then removed it, lol). With 6.1's stronger CC and weaker healers, it's no longer required to effectively pressure kills, but I don't think it ever hurts—if your switch is clean and committed enough, it can often kill players before they have the opportunity to Guard or Purify.