The problem of the focus, is that you have to re-focus your target after each loading, even a small loading within the same dungeon, like the trash bin in Castrum, or a wipe.

When you think about it, it's not a big deal, but when you forgot, you may have issue noticing it mid-fight when your heals don't reach the tank.

They really need to change this system, and keep the same focus for all the duty, unless you manually change it. For some dungeons, like cutter's cry, it's really boring, losing your focus every 2 packs.