on the Elemental data center, during every WoD run i have done, we use melee DPS LB3 during or around the 2nd cloud phase, i say around because sometimes other alliances manage to get 3 bars before the 2nd cloud phase starts and they start building up more bars
the only time i have ever had to use tank LB3, was when WoD was new and people were messing up 2nd cloud phase because people didn't know what was happening