@Bill.Oliver obvioulsy, licensing.
If you are planning to put Microsoft VMs, beware of licensing with multisockets by hosts, you have to cover them all.
By default, you should cover 16 cores with 1 Microsoft Windows Server Standard to get 2 VMs licensed.
If you get two sockets, you have to double the licensing (and add 2 packs core to attain your cores coverage...)
All licensing based on cores make you think twice when planning CPUs...
If you want to, you can go DATACENTER edition, but you still have to cover all the cores...