Why Placeholder Datastore is not required for Storage Policy Based Protection Group (SPPG) in SRM 6.1?

Q. Why Placeholder Datastore is not required for Storage Policy Based Protection Group (SPPG) in SRM 6.1?

Answer :- For storage policy based protection groups, Site Recovery Manager applies inventory mappings to virtual machines when you run a recovery plan that contains a storage policy protection group. With storage policy protection groups, because storage policy protection is dynamic, Site Recovery Manager only applies the inventory mappings at the moment that you run a recovery plan. Virtual machine placement decisions are made according to the inventory mappings when a recovery plan runs, so Site Recovery Manager does not create placeholder virtual machines on the recovery site

With array-based and vSphere Replication protection groups, Site Recovery Manager applies inventory mappings at the moment that you configure protection on a virtual machine.

For More Info refer VMware Documentation:-
http://pubs.vmware.com/srm-61/index.jsp#com.vmware.srm.admin.doc/GUID-03648A26-A86C-46B6-8748-4ED112755AA1.html