No one should ever dispute a proper LB usage. If they do, you immediately know they're an idiot and can probably kick them just for the "harassment", as they're some of the most vitriolic people I've encountered in game.Here we do a FAQ on LBs:

1).Why do dps wait so late to use LB? If they're good, its because they're trying to see if they can squeeze out another bar for a higher LB rank. If they're bad, its because they're not paying attention.

2).What's the difference then? The bad player will never use it, or uses it way too late. The good player realizes towards the end that it won't happen and blows it early enough to ensure all the dmg counts. Ideally you figure this out early enough to push the target into execute range (the point at which abilities like mercy stroke can be used to increase the dmg dealt), not after its already there.

3).Why should it always be Melee who use it? It shouldn't. If we're talking a single boss then yes, it's on the melee (unless one isn't present) as being chiefly responsible. If we're marching through trash and it fills, its on the Ranged to use it for an aoe pack. If we're on a boss with adds, it's again on the ranged due to the possibility of lining it up for multi-target hits. Under no circumstances should an LB go completely unused though.

4).But all the bars are filled and that idiot isn't using it! Are you a dps class? If so, use it yourself. If not, say something in chat. Count to 10. If still no response, its Healer/Tank LB time to punish them.

5).But I'm <insert your terrible class here>, I shouldn't have to use it! It's too much of a dps loss for me! WAHHHH!!! Use it yourself. No single player's damage outweighs the gain of the limit break. Furthermore your class doesn't matter, lowest dps always has the responsibility to LB, unless they're too braindead to know.

6).Ok I see your point, but Scrublord McJagger over there just bit the dust and got rezzed... If Sir Scrublord is dps, tell him to use it. Weakened players are always low man on the totem poll and have the responsibility to use LB. If he doesn't listen within 10 seconds... Use it.

7).So you're saying it's basically always my responsibility? Yeeeeep. LB's responsibility is shared amongst the group. Just because one guy is too stupid to use it doesn't get you out of the responsibility.

Note:It's worth waiting til a good point in your rotation sometimes. As a BLM, I often do my multiFlare combo and then hit the LB during my umbral ice recovery.