When would you need to create an additional vDS?

There is a lot of discussion of how to create a vDS, but I cannot find the discussion of when you should create an additional vDS.

We are all NFS based datastores, so we are thinking of creating one vDS with the storage NICs and another non-storage vDS.

But that might just be more management overheard.

Support personal and general discussions with sales folk indicated that this should not be necessary. Asking "How many vDSes do I need" always seems to get the answer "One", so I thought I would try the question the other way: "Why would I ever need more than one?"

Note: VMware increased the number of vDS per vCenter Server from 32 in 5.0 to 128 in 5.1, so someone must need more than one.....