I don't really want to continue the argument, but I just have to say this.
I think a lot of the advice here was good. Someone mentioned that Lucid can usually be timed to manage your MP and drop aggro, killing two birds with one stone. That's absolutely true.
The problem is rarely healers because Lucid is so essential to MP management.
The problem is DPS like BLM, who never use Lucid because they don't need it, so they save it for a panic button. They don't realize that if they were to use it (and Diversion), a tank would gain a roughly 21% DPS increase over the course of a dungeon. That's huge, and it absolutely is better in the long run.
The above isn't even the BLM's fault. A lot of DPS end up in bad pugs. In these cases, saving Lucid as a panic button is the smarter choice.
But it's not the smarter choice when you have a group that's trying to optimize their clear times.
And again, no one's at fault because it's impossible to predict how good X pug tank and Y pug healer will be if you use Lucid right now. And a lot of DPS are afraid of being blamed for stealing aggro and dying while Lucid/Diversion are on CD, which is a legitimate fear.