One can guess. Staging is used to show what would happen given a specific setting. Tightening on the other hand allows you to find more specific settings to refine your policy.
Settings in tightening are not to be enforced, but rather are for clarifying your policy elements only. It doesn't make sense to say "I want to see suggestions for more specific settings, and I also want to stage this generalized setting".
In general you can use tightening to identify specific policy elements, then you stage your specific changes until you're comfortable with them.