When you delete a site in Sakai, there are two different types of deletion: Soft Delete and Hard Delete.
Soft Delete is the default deletion method, and can be done from either the Sites tool in the Administration Workspace, or the Worksite Setup tool for users with deletion permissions. Soft Delete removes the site but leaves site data intact in the database and file system. There is also job that administrative users may run in the Job Scheduler tool to purge any softly deleted sites in the system.
Hard Delete is an option for permanently removing both the site and all of its data from the system. This option can be done in the Worksite Setup tool for users with deletion permissions (typically admins only). Hard Delete is used when an institution wants to free up space on the server by completely removing old site files and data.