I came across your thread while searching for the same answer myself.

I have worked in various environments and generally additional vCenters have only been created when there is a specific need E.G. different site or different environment (secure environment separation etc).

Having also worked in some large enterprise / managed service provider environments I have noticed quite a lot have separated out their management and compute utilising separate vCenters, however I am yet to understand why / what is the benefit. Even with NSX and other product integrations as long as the clusters are separate (which I completely understand and agree with) I fail to understand or agree on why vCenter separation is required.

Now saying that, if you are not running VCSA 6.5+ and taking advantage of vCenter HA I can appreciate that having them separate gives you a bit of a safety net but really nowadays is it necessary to have them separate?

I have yet to come across or think of a solution that would specifically require this separation, has anyone else? Responses from Architects and VMware would go down a treat