About DataStore TM between Image and System

Hi:
I have some doubt about TM between Image and System. For example two datastore:

ID NAME SIZE AVAIL CLUSTER IMAGES TYPE DS TM STAT
105 Image 241.7G 95% sjhl 1 img fs shared on
107 NFS system 0M - sjhl 0 sys - shared on

Image --> BASE PATH : /var/lib/one/ds/105
NFS system --> BASE PATH : /var/lib/one/nfs/107

I add a host and download the ttylinux-kvm template on Image datastore, then i init a vm and deploy the vm to the host. I find the vm disk not in /var/lib/one/nfs/107 ,but in /var/lib/one/datastores/107 ;
then i add the host to a cluster and set cluster DATASTORE_LOCATION=/var/lib/one/nfs/ the vm disk will be on there. What the BASE PATH purpose of system datastore ? only use DATASTORE_LOCATION ?