SQL Server on VMware why 3 vnics We have VMWare ESXi hosts administered in VMware vSphere.  I've sent my network admins this artice, http://www.sqlservercentral.com/articles/Virtualization/125226/
and asked what they think.  Currently our SQL Server VMs have one vmnic.  They wonder why the article is suggesting 3 when according to them that's redundant.  See their email that I've anonomized and shortened below.  

"The author isolated SQL frontend traffic, availability traffic, and backup traffic. Since the vmnic does not have a hardware speed limit, multiple NICs will not increase, according to our VMWare expert, performance. What other reason would there be to separate out these VLANs? We currently have a flat network within the datacenter, so unicast traffic between these three VLANs would not be limited by default. Broadcast traffic would be confined to the VLAN."

I'm wondering if this is necessary and/or recommended, and if so why? 

Thanks in advance,
The three NICs won't help with redundancy, because the VM layer should have already handled this configuration under the hood in the virtualization layer itself.

However, three NICs would allow for segregation of particular types of server traffic (backups, AG replication, etc.) away from the primary NIC, which allows you to monitor and profile the usage patterns of these NICs better.