Numerous tactical uses for Purifying Chastisement exist. It provides the Inquisitor with one of his utmost essential abilities and greatest powers.
To be blunt - using this buff REQUIRES the Inquisitor to take damage. Playing too defensively will only limit the ability to use this buff to its fullest extent.
Note that, like all CA's in the Gruesome Inquisition aspect, casting speed is determined by weapon speed, and can be boosted by weapon lore skills and +% attack speed. Likewise, the casting speed will be penalized by wielding a weapon with too high a level.
The Bronze level modifications are seemingly superficial, but they actually have very specific applications.
Purge is better used for Inquisitors who wish to use long ranged weapons, slow melee weapons and/or make use of damage over time.
Mystic is better for Inquisitors who wish to fight up close and personal, utilizing fast melee attacks.
Note that these two modifications do not add fire or magic damage, they multiply existing damage of that type. So if the Inquisitor is not wielding weapons with either of these damage types, they will not take effect. Note also however, that these modifications also apply to spell damage, so for example, the magic damage of Levin Array will be boosted by Mystic.
The Merciless modification is good for a player who is more concerned about defense than offense. Bloodthirsty, reckless players are better suited with Eradicate.
The critical hit boost caused by Eradicate is incredible - for example, at CA level 12, Purifying Chastisement will give the Inquisitor an extra 11% chance to cause critical hits.
The reckless, hand to hand Inquisitor will thus find this to be more to his liking since he will most likely be using rapid, quick hitting attacks.
As with the above, Inure is intended for an Inquisitor desiring more defense. Hallow is the crowning glory for Inquisitors wishing to push their damage to the max.
It is NOT recommended that an Inquisitor chooses Combat Reflexes if he intends to make maximum usage of Purifying Chastisement.
The Inquisitor WANTS to take hits while he is under the effect of this buff. Getting hit less will make the Inquisitor do less damage.
The Inquisitor, by default, has a very high Dexterity growth rate. Suffice to say, his capability to evade is already better than average.
Spell Resistance is a better choice due to the fact that it makes up for the Inquisitor's very low Willpower growth rate.
Spell Resistance is also recommended since it will still let the Inquisitor get a chance to evade critical hits, but not the melee hits that fuel his anger.
It is highly recommended that an Inquisitor acquires Constitution as early as possible, if he is going to use Purifying Chastisement.
This will allow the Inquisitor to not only allow greater blows to fuel his anger, but also allow the Inquisitor to quickly regenerate his life in the event of receiving numerous hits.
As you may (or may not have guessed), the increased HP and HP regeneration rate can easily give the Inquisitor a way to shrug off melee critical hits.
Armour Lore is recommended since it will help the Inquisitor lower the regeneration time penalty caused by armor weight.
This is especially helpful for Inquisitors who intend to make Gruesome Inquisition their main aspect. The reason being that the Gruesome Inquisition oriented armor tends to be heavy.
Toughness is not recommended to use with this buff. Similar to the case with Combat Reflexes, Toughness lowers the Inquisitor's damage intake.
Inquisitors concerned about damage mitigation, but who still wish to use this buff should take the Inure modification.
Also note that Armour Lore can provide tremendous armor/damage decreases on its own, and when Armor Lore Mastery is acquired, rare caliber armor with inherent damage mitigation can be used.
Pros and Cons
Almost mandatory for any Inquisitor who will be engaging in melee combat; this buff is one of the Inquisitor's most defining and powerful features.
Offsets the Inquisitor's inherent lack of of defensive capabilities. This buff gives him tremendous damage boosts.
Relatively low regeneration penalty when activated.
Can also be used on a more defensively minded Inquisitor due to the Inure modification.
Due to its nature and importance to the Inquisitor as a whole, efficient use of this buff can require a certain play style.
Therefore, if a player wants to use the Inquisitor in a manner that does not entail taking damage, this buff is perhaps not for them.
Enemies that can debuff the Inquisitor will make battles take much longer (or in some cases, less survivable).
The Bronze modifications for this buff can force an Inquisitor into limiting his elemental damage variety.