Hello, I can tell example where having raw disk as PV is handy: using hardware RAID controllers, such as Areca ones.
Raid controllers allows you to add new disks to existing raid array. For example, if you have Raid 10 using four 1TB disks, you can add two more disks and increase capacity from 2TB to 3TB. After raid *online* reinitialization, one can increase volume size inside that raid array, and system now can see that /dev/sda is incresed to 3TB, also without downtime (simply after rescanning SCSI). Now, if you have LVM PV inside partition, you first have to resize partition first, which will mean downtime and possibly disaster on human error while fiddling with partitioning tools. Meanwhile, if PV would be a physical disk, one could simply use pvresize...
