When set to true, the activity will run continuously, even when there are no matching Messages. When there are no matches, the activity waits until a Messge arrives. When set to false, the activity completes when there are no matching Messages.
Make sure that your workflow does something to the matching Messages so that they no longer match. Otherwise, you will create a loop.
Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2