You kind of assume that enmity +/- has no influence on pvp where it could effect it in a way you haven't thought of yet.

In FFXI's Ballista, Provoke was used to force a target to only be able to attack/cast magic on you.

XIV has 3 "Hate grabbing" abilites
Provoke/Taunt/Flash

Enmity+=Increases the duration of forcing the target to attack you
Enmity-=Decreases the effect of Provoke/Taunt/Flash

So WHMs who may be the target of a Voke/Taunt/Flash can wear -enmity to decrease the duration of a forced target so that they can get back to curing their allies again.

While a PLD/MNK/WAR can use +enmity to increase their timer when forcing a target to attack them.