When your melee pop lb3 at 10% you can be sure something wrong will happen at before your team can finish off the last 3% resulting in a wipe/ enrage.

On the other hand everytime you hold it until the very last minute not only no one fail but melee entirely forget to use it. (this si where I do lb3 heal)

As a side. It note any lb3 heal will result in the death of the healer.