When the --blog parameter is passed, it would trigger a call to switch_to_blog() (if multisite is enabled).

The command that would benefit from this most is theme activate, since setting up a theme for a particular blog using the normal MultiSite admin is very long-winded.

Example usage:

wp theme activate a-new-theme --blog=newblog

Ideally, you could pass the blog slug and not the blog id.