It's more of a restart from a user perspective. The primary use case if for dynamic vdbs that have metadata updates. You want the runtime state to be updated as well, but you're current options are to restart the server or to redeploy the vdb.xml. In the latter case unless we provide a good mechanism to get the current server version of the vdb.xml and reploy it, then we're asking the user to track any admin modifications (to data roles, date sources, etc.) some where else - which seems unnecessary.