vSphere Replication Guest OS Quiescing

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http://serverfault.com – I am using vSphere Replication 5.1 to send virtual machines off to a separate datastore every 24 hours. One option in configuring each VMs replication is the Guest OS Quiescing option. Options are None and MS Shadow Copy Services (VSS). I not sure what the pros and cons of this option are and can't find much information explaining it. Anyone have any experience with this? (HowTos)