What are some situations where annulment would be preferable to divorce?
Just to be clear annulment is the remedy where a marriage is voidable rather than void.
If a marriage is void it is treated as if it never happened.
If a marriage is voidable it can be voided if either party wants to push for that. A classic example is lack of consent due to intoxication. Both parties to a marriage can quite happily continue in a marriage that went ahead when one of the parties consider they were to drunk to consent, but afterwards are content the marriage should stand.