Tanks will be automatic and as long as the party is within the vicinity of using the LB, it will grant all party members near by the tank (when the tank clicks the LB) to auto grant bonus xDefense.

Melee dps LB has to be in the range of the mob with your melee skills. If you can't touch the mob, you need to be closer for the LB to activate, but you would target the mob and hit the limit break skill.

Ranged DPS is a distance matter and shows a solid blue line across the field. You NEED to be targeting the mob to use it. Otherwise it will not operate. For the wings on Bardam, the tank needs to keep the mob still and not turn the bird at the end. Otherwise, you could potentially miss both wings and waste the LB.

Magic DPS brings a circle. If you want to know where the circle is, try using the marker system A B C 1 2. This will give you an idea of where the circle is on your current screen, but you can make easy adjustments. You can still bring it up as long as the LB is active or has at least 1 full bar available on the battle field. You just need to adjust this manually. This does not need to be targeted on a mob to use it. But you do need to be able to see the circle with your cursor and/or controller and thumbsticks. So play around with the marker system so you know where it will auto appear on your screen, and that should help quite a bit outside of instances.

Healer LB requires the healer to be in the vicinity of its party members, similar to tank LB. It can actually miss players on the field since it's yalm based and within distance to the players. If the healer is LB'ing on the other end of the field and your character is dead on the other end, you won't be raised. It's not wide arena like some boss mechanics are (Rabanasty for instance). So when using it, as long as you're within each member and know where all members are, it should auto hit everyone at once who's dead. Just keep that in mind.