It depends on VMware Fusion snapshot functionality. As such it is not a problem to make backups of a running virtual machine. The way it works is that it makes

It depends on VMware Fusion snapshot functionality. As such it is not a problem to make backups of a running virtual machine. The way it works is that it makes a temporary snapshot of the VM when it is running. Parts of the disk from before the snapshot are now closed and new data is written as Copy on Write. The data that is safe to copy (which includes your VM state and memory) is then copied to your backup location. After Vimalin is finished copying the data it will also commit that temporary snapshot. On restoring a backup it gets back to the state from before the backup started, just like with a snapshot, except this was written on an external disk. You can schedule when it is convenient for you to run the backups. Like Time Machine it makes full copies of the disks. But because you can schedule how many copies you want to keep you can prevent your backup storage from getting overrun.