A question came up on the forums a little while back about the above registry key which can be added to the Enterprise Vault Server.
Essentially the key can be used if you want to the Exchange Archiving Task to rebuild every single shortcut it encounters. This obviously has a performance impact, and should not be used without consulting with Support, and tested thoroughly in your own lab environment.
It is useful to use it in the early stages of rollout, perhaps, when the contents of a shortcut (or the required contents of a shortcut) needs to change because the business needs have changed.
The key is described in the references below.