It's more about the best practice when it comes to VA.
Umbrella document mentions that only one VA is required per site. However, they recommend having an extra for redundancy purposes.
From the guide "Note: Only one connector is required per Umbrella site, with an optional second connector for redundancy if required. If you are onboarding multiple AD domains through domain controller integrations, one connector is required per AD domain per Umbrella site, with an optional second connector for redundancy if required."
If you find this useful, please mark it helpful and accept the solution.