>I didn't say he shouldn't use it as a candidate index. If he needs to keep that combination of fields unique, and as long as they aren't used for a primary key, or updating, or a relation, what would be the problem? Is it a question of reverting correctly in a heavy multi-user environment?

Sorry, I read you response too fast. As long as he don't use a composite key as a primary or candidate key, in my opinion, there's no real disadvantage of using it.