Canceling a deployment tells the Configuration Manager to assume that a broker will never respond to an outstanding deployment.
You might need to cancel a deployment because the Configuration Manager allows only one deployment to be in progress to each broker at any one time. If for some reason a broker does not respond to a deployment request, subsequent requests cannot reach the broker, because, to the Configuration Manager, a deployment is still in progress.
If a broker subsequently does provide a response to an outstanding deployment that has been canceled, the response is ignored by the Configuration Manager, and an inconsistency subsequently exists between what is running on the broker and the information that is provided by the Configuration Manager.
Because of this risk of inconsistency, cancel a deployment only as a last resort, and only if you are sure that a broker will never be able to process a previous deployment request. However, before canceling a deployment, you can manually remove outstanding deployment messages to ensure that they are not processed.