I've been a JIRA and Bugzilla admin in past jobs, and have quite often had users ask for the ability to have more than one assignee per issue.

I know this is possible in JIRA, but to my mind it never makes sense; an issue should represent a piece of work, and only one person can do a piece of work (at least in software, I've never used an issue tracker for a 2-man bobsled team ;-)) A large piece of work will obviously involve more than one person, but I think in that case it should be split into subtasks to allow for accurate status reporting.

Does anyone have any use cases where it's valid to have multiple assignees ?