@iosonopiero, the type of storage you choose depends on your goals, e.g. RAW storage focuses on performance, while thin provisioinig targets the efficiency of space allocation, and a file-based storage can provide flexibility including live snapshots, live migration, etc.
Also keep in mind that hypervisor is basically a role you can run remotely, and libvirt allows connecting to remote hypervisors and manage both local and remote hosts and guests the same way, so carefully delegating this role can significantly affect the backup strategy.
@computersavvy, you are confusing system and session modes, and the latter does not require privilege elevation to access and manage the storage pool.