Sleigh said it, it not only covers the damage, but prevent the sludge puddles. In fact, the negate of puddles is the thing here. However, I disagree on DRG beeing one of the lasts on Cover priority. I can think this is correct if your static has a MNK (who may have a major DPS loss due to disconect), but in my case, we have DRG(me), SMN, BLM and BRD (wrost dps setup, lol) so the PLD will look for me on the first Earthshaker. If I'm not targeted, he won't cover anyone.
For the second (if he didn't covered my on the first) he'll look to me and our BLM, but he'll cover the BLM only if I'm not a target. The BLM sure has a DPS loss, but less the me. For BRD and SMN, they can handle it and keep dpsing.
But it may vary, depending on several factors. For eg, if someone on your group has latency problems, or if your melee has a crap gear and you have a top BLM doing the most of the damage, and so goes on but in a fair dps competition, I think a melee should get covered.
