The current Vagrantfile (v2.1.0) configures VirtualBox to use a linked clone:
vb.linked_cone = true
According to Vagrant's docs, this defaults to true for the VMware provider- which is why it has not been explicitly configured in the Vagrantfile.
But.. after my experience with Vagrant, I simply can not trust anything they claim these days. Confirm whether or not this is true. If not, then please configure linked clones for VMware as well.