It will allow Team Foundation Server work items to be synchronised with Jira. The idea is that business user that already use Jira implementations will be unwilling to move to the more comples Team System. This will allow them to contiue in familiar teritory, while providing the developement teams with the advantage of TFS.
I would happily donate my project ( http://www.codeplex.com/TfsWitToJiraSync
) which I do not have time to work on.