Biggest benefits I see are:
Granular storage policies per VM, so you could for example assign a policy to a VM to be on flash storage and another VM or VMDK to be on slower storage without having to worry about datastores at all.
From a management perspective, the Datastore concept is old. Mapping 1 LUN to 1 Datastore is just a waste of time. Datastores run out of space too, so getting rid of this LUN to Datastore mapping makes a lot of sense to me, no longer do we need to "Make sure there is enough space on the datastore to provision a new VM, or to storage vMotion"
The VVOL concept is not new, but the integration into production storage arrays is relatively new so I would be very careful when selecting a vendor.