When designing your boundary strategy, we recommend you use boundaries that are based on Active Directory sites before using other boundary types. Where boundaries based on Active Directory sites are not an option, then use IP subnet or IPv6 boundaries. If none of these options are available to you, then leverage IP address range boundaries. This is because the site evaluates boundary members periodically, and the query required to assess members of an IP address range requires a substantially larger use of SQL Server resources than queries that assess members of other boundary types.
Note : Taken from Technet AS-IS