This second blog by Altaro dealing with Hyper-V backup discusses when Application-Consistent Backup is vital for proper recovery or not. What if a VSS Writer is not available for a particular application? What are the general requirements for Application-Consistent Backups in Hyper-V? What are the Special Considerations for Cluster Shared Volumes?
When is Application-Consistent Backup Vital? Not all situations require an application-consistent backup. Things such as file and print servers will be fine with crash-consistent and possibly inconsistent backups. If your application doesn’t provide a VSS writer, there might not even be a way to get an application-consistent backup of it while its containing machine is live. The most common need for application-consistent backups is the usage of database-backed applications.
The full blog can be found here: