Generally the DPS would use it as soon as they can, unless it is incorporated into the strategy (I have seen ranged using the line LB in A1S at an optimal time). The rule of thumb is to use it when you can (as a DPS) within the confines of your DPS rotations, i.e. dont do it when its going to ruin your DPS, its not worth it.

As for healers and tanks, their LBs are much less useful in high end content as healers are A) risky to pull of without dying themselves, and B) you are likely not going to meet the DPS check anyway. And as for tanks, its really not needed apart from particular fight phases.