Microsoft provides the Cluster Validation Wizard feature, which is important for two major reasons. The first is that it can help you identify issues that might cause problems for your cluster before you even create it. The second is that Microsoft is only committed to providing support for a cluster that has passed validation tests. If you need to contact Microsoft support, they may decline to aid you with a cluster that has not passed.
Validation should be performed prior to the initial creation of the cluster, but it should also be performed after most cluster configuration changes. Major events that warrant a new validation report are the addition of a new cluster node and connection to a new storage device. However, minor modifications such as driver upgrades and even Windows updates will also invalidate the existing report. How closely you keep your validation report current is a risk balance that is up to you or your corporate policies....