As per my understanding yes this the last best practice guide release specifically based on VMWare,
https://h20195.www2.hpe.com/v2/getpdf.aspx/4aa4-7060enw.pdf
Coming to the portion that you have highlighted, this is just an ideal example but that doesn't mean everyone wil follow this.
Obviously if anyone having single pool, single Virtual Disk Group and multiple volumes created. Those volume presented as datastore in VMFS. On those datastore each having multiple VMs running then performance impact will be there compared to single pool, single Virtual Disk Group and single volume where few VMs running.
Ofcourse tiering is important. It depends on what type of drives that you are using. In ideal system you should have Performance, Standard and Archive type of drives so that respective type of VDG can be created under same Pool.
You can also check volume affinity feature and that can also help for specific purpose.
Hope this helps!
Regards
Subhajit
I am an HPE employee
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