Since Berserkers have a lot of damage potential but in return take an equally large amount of damage. The Guts effect of this CE helps alleviate some of the risk that comes with fielding a Berserker. In comparison to using healing effects Guts will allow you to survive any hit, even if the damage is more than or equal to your HP in exchange for only working once.
For tanks, this CE can be useful as a safety precaution when the tank doesn't have access to their suitability skills (Dodge / Healing). In situations where the boss gets access to their NP quickly, Guts allows the tank to survive through it.
Chauvelier d'Eon Arash Ibaraki / Berserkers
Similar Craft Essences
Table here: CE Picture -- CE Name --- Effect
Necromacy Chaldea Lifesavers Princess of White Roses