If the outreach sequence is in progress, and you add the site to a blocklist (Global or Project specific) from the Opportunity Details page, this will pause the sequence in this instance, and change the Workflow Status to 'Finished'.
However, if the outreach sequence is in progress and the site is added to the blocklist manually (from Settings, then Prospecting Blocklist), this will not pause the sequence.
This is considered a manual action and tells the system not to discover the designated site during prospecting.