What is an Enhancer?
An Enhancer is the support class of the game. Capable of throwing down shields, attack buffs, defense buffs, and high level cures -- they are the lifeblood of any party. Focusing primarily on a high level of Intelligence to achieve these buffs as well as increasing their support capabilities, purebred enhancers are by no means capable of damage without relying on their demon or on others.
Advantages of an Enhancer
Mana Pool - Capable of holding the most MP out of all the classes because of their necessity to have high INT.
Cheap Equipment - With fairly cheap and easy to produce Soul Stones, there isn't much equipment that an enhancer absolutely needs. They can essentially wear whatever they want because of this.
Hybrid Potential - Enhancement is the one chain expertise than can hybrid into any class. Melees, Gunners, and Mages all have the capacity to hybrid into this class.
Disadvantages of an Enhancer
Consumables - Enhancers tend to expend their large MP pool fairly quickly. As a result, enhancers eat up a large amount of enhancement beads and MP restoring items.
Support Magic - A variety of buffing skills are in here ranging from boosts to CLS-R to nullifying expel or death-based damage.
Curative Magic - This skillset allows the caster to remove status ailments, restore HP, and even revive dead party members.
Enhancement - Allows the caster to heavily reduce the incoming damage from enemies or boost the damage allies produce for a short amount of time. Also allows for an extremely wide-reaching AoE healing spell as well as reflective shields.
Curse of the Wretched - A chain expertise that's a great supplement to an Enhancer. It induces a wide array of debuffs and status ailments on opponents and allows their allies to take advantage of the weakened enemies.
Retaliation - Specifically using the Lord of Armor Toggle -- obtaining this chain expertise can turn any enhancer into an nearly unkillable tank in exchange for completely removing their damage capabilities.
Enhancers typically hybrid into just about more than one chain.
Retaliation Enhancer: Pure and total support capable of throwing down a wide array of buffs without being killed easily. The ultimate tank.
Enhancer Curser: A Pure Enhancer that has hybrided with Curse of the Wretched and can not only fully support the party but throw down debuffs that can make the toughest boss squishy.
Of course, you'll see enhancement being mixed with just about every other class as well. However hybriding into those classes generally prevents someone from using the end skills of the Enhancement Chain which can prove to be quite a lifesaver.
Essentially anything that boosts their INT as well as reducing the cooldown and cast time of their spells.