had to close the site a few minutes, the database this site rely on got an upgrade, and was moved from one server to another as well..
Before the upgrade, the WP-optimizer plugin was run (to ensure that the cruft was removed). After the upgrade, an additional run of WP-optimizer did show: Total Space Saved: 13341.883 Kb
Why the difference between before and after the upgrade? The databases are equal – and the site was down during the upgrade..
Don’t know why this did happend, so a question is sent.
The huge amount of spce saved was because a table got wild. To fix the bug, the table was removed – and the table + content got reinserted.