Altaro has posted the second part of their series on VSS Crash-Consistent vs. Application-Consistent VSS Backups. You can find the first post here. In this post they discuss:
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.
Give it a read to learn about backup from a backup developer.