Chaos magic is very useful for elves, especially on maps with dragon utopias and places where powerful artifacts are found, because the probability of finding a Chaos tome is very high. I picked it up three times in the last week, which I can't say about other tomes (Summoning never dropped for me), on the road, and twice in utopias. If I'm playing on a map without these places, I don't take it, because in the guild, I practically never find good Chaos spells.