I recently conquered the Ashen Veil holy city, with their holy shrine. I decided not to raze the city, but to conquer it instead. However, I do not have much use for the entropy mana I got from the Veil shrine, certainly the diplomatic penalty is worse than the usefulness of the entropy mana for me currently. So, I decided to use diplomacy and gave the entropy mana as a gift to the Ljosalfar. The result is that the elves like me because I gave them a gift, while everyone else hates the elves because they use entropy mana. In this game the overcouncil shortly afterwards banned entropy mana which ended that trick, but giving entropy or death mana as gifts could be used undermine the diplomatic positions of your rivals, and if you need the mana yourself you can always end giving the mana.