Setting failover policy at the port group level vs. at the virtual switch level

How does setting a failover policy at the port group level differ from setting it at the virtual switch level?

For example, I am setting an active / passive failover policy.  When would I set it at the port group level, and when would I set it at the virtual switch level?

If I am setting active/passive at the port group level, would I then use active / active at the vswitch level?  Or would I set both the port group and vswitch to active/passive?

Thanks!