There are use cases where you need to reset the node numbering.
For example, lets say you have 100 nodes and you delete 10 of them. By default, the next node ID will be '101' even though '91' to '100' no longer exist.
This is actual quite easy to fix, but it has to be done in PHPmyAdmin instead of Drupal
1. Log-in to PHPMyadmin and select the database for your site.
2. Go to the table node
3. Go to Operations tab
4. Locate the group "Table options"
5. In this group is a textfield called AUTO_INCREMENT. Simply pop-in the new ID number. In the example above, you would set it to 91.
6. Hit submit.