This permission was introduced in Exchange 2000 and provides the capability of "administering an information store". That's a pretty non-specific permission, but that's what all the available Microsoft documentation says about it. See, for example, here Unfortunately, there is no available public documentation that fully defines this permission and/or what capabilities it may allow. I [...]

As of April 10, 2012, Exchange 2007 has entered the Extended Support phase of our Support Lifecycle.This means going forward Microsoft will provide only security fixes for it. No Hotfixes will be provided unless there is an Extended Hotfix Agreement (the only exception is if changes are needed for support of Exchange 15 which will support Exchange 2007 [...]