When you clone a website or pull a database from Cloud Platform to Acquia Dev Desktop, you can optionally sanitize (or scrub) the database of user emails and passwords. This is a best practice for security, so that your local website never includes real user emails (to prevent developers from accidentally emailing users) and passwords.

Selecting the Sanitize database checkbox is the equivalent of using the --sanitize option with the drush sql-sync command. By default, it changes all email addresses to user+%uid@localhost and changes all passwords to password. You can customize these operations by editing your ~/.drush/drushrc.php file.

If you have installed contributed modules that use the hook_drush_sql_sync_sanitize function, selecting Sanitize database in Acquia Dev Desktop will also execute any sanitizations provided in those contributed modules.