Blacklisting vs. Deleting
During the any stage of the workflow you can add one or more opportunities to the Blacklist, by first selecting those opportunities then clicking the drop-down arrow next to the 'Delete' button and selecting 'Project Blacklist'. If you are an admin, you will also see the option to select 'Global Blacklist' (for more on the difference between Global and Project level Blacklist you can check out the article here!)
If you are an Admin you will have the option to add to the Blacklist by clicking 'Settings' then 'Prospecting Blacklists' at the top of the screen.
From this screen, an Admin has the ability to add to or remove from the blacklist on an account-wide level, or at the project level using the drop-down menu.
When you blacklist an opportunity, it will not show up for any future campaigns in that project. If you delete an opportunity, you are only removing it from the campaign and it could reappear in future prospecting campaigns.