Backups are independent from your VM and can be stored everywhere like every file.
Snapshots are in your VM-disk so you cant take it away.
Backups are full copy's of the VM and need more space
Snapshots need less storage.
Backups would take more time.
Snapshots are instant.
By using Proxmox VE live snapshots you can preserve the KVM virtual machine state. A snapshot includes the contents of the virtual machine memory, virtual machine settings, and the state of all the virtual disks. When you rollback to a snapshot, you restore the memory, virtual disks and all settings of the virtual machine to the state they were in when you took the snapshot.
You can take a snapshot and continue to use the virtual machine from that point, take another snapshot at a later point, and so on. You can rollback to the snapshot of a previous known working state of the project if the changes do not work as expected.
Before a backup can run, backup storage must be defined. A backup storage must be a file-level storage, as backups are stored as regular files. In most situations, using a NFS server is a good way to store backups.Backup modes