Teamness gives you the option to archive a project. This makes the project read-only, meaning that you can only list and view the items in that project, but not edit, add or delete. Also, all the members of the project, except the owner, are removed from the archived project.
You may want to archive a project when it has no more activity, for instance when it ended or when it's in a paused state. If your pricing plan requires a limited number of active owned projects, archiving an old project will allow you to create one more active one.
You can also make back active an archived project, but please note that if you reached the limit of your pricing plan with the number of your own active projects, you cannot make a archived project active again. To do so, you will have to either archive another project, delete an existing active one or upgrade your pricing plan.