minimum-reserved-bandwidth setting in ACL

A few questions about this parameter.  It would be great to get some clarification on the setting.  Is it more to set to during and registration avalanche or some other type of flooding, it reserves the bandwidth for the session agents so the public side won't take it all during the storm?  Can you give some advice on how to calculate what it should be set to, if we decide to set it?  I assume it is based on the amount of signaling done to the SA, but don't really know where to start in coming up with the calculation