This is standard definition in case of SATA disks, NVM, SSD each have own defined partition names if so to be called, this is based on the number of disks you use in your environment.

For example if you would have a setup with NVM disks the namming will be different yet the names again will be defined by the physical number of disks visible to host.

root@sc:~# fdisk -l
Disk /dev/sda: 446.6 GiB, 479559942144 bytes, 936640512 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0xcc24555f

Device     Boot     Start       End   Sectors   Size Id Type
/dev/sda1  *         4096   1050623   1046528   511M 83 Linux
/dev/sda2         1050624 457766911 456716288 217.8G 83 Linux
/dev/sda3       457766912 458813439   1046528   511M 82 Linux swap / Solaris
/dev/sda4       458813440 936630271 477816832 227.9G 83 Linux


Disk /dev/sdb: 1.8 TiB, 1999844147200 bytes, 3905945600 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Now as you can see I have here 2 disks in use, SDA a SSD in this case and SDB a SATA disk. SSD/sda is used for OS while sdb its pure storage.

Hope this clears out the fog.

For a proof of concept cloud, there is no benefit.

Or perhaps I misunderstand the meaning of "OpenStack examples". If so, please clarify.