GEO Jobe has improved the Delete User functionality.
In the Native ESRI User Interface, if you were to attempt to delete a user that owns content, you'd be blocked from doing so until you have manually moved or deleted that content. With the Admin Tools Delete Users tool, when you attempt to delete a user and it still has content, you are presented with a popup option to either: (a) delete everything they own, or (b) move that content to a new user, and then proceed with deletion.
Video on Delete User Improvement
STEP 1: After Selecting the Delete Users tool, filter and sort as needed, and select the users you'd like to delete. Click Next.
STEP 2: Review the Confirmation screen for the users to be deleted, and click Done.
STEP 3: Select the option to delete all content along with the user, or move that content to a different user, either by typing in their name (with auto-complete) or selecting the user from the drop-down.
This tool is available in both the Basic and Pro Version of Admin Tools.