Here is the basic difference between posture policies and client provisioning.
Posture: These are policies that are related to any sort of program/files/updates/etc. that exist on the client.
Client Provisioning: These policies are really only related to Cisco AnyConnect or posture modules from ISE.
For example you may have a posture policy to check AV status, and if the endpoint AV is out of date you might put it in a VLAN where it can only hit the AV update server. Once the AV is up to date the endpoint is allowed normal network access. Now you have a client provisioning policy to push out the XML file for the AnyConnect corporate VPN connection, it sees that the endpoint doesn't have the correct XML file and now the client gets the updated XML from ISE.
Hopefully this gives some clarification between the 2 policies.