How important is having a database optimized. Doing some "basic" optimizations like clearing the cache, runing the Drupal cron and a couple of things more, your database can change from having 4 GB to just around 200MB... incredible? Not at all, the importance of maintenance tasks :-)
Which tasks? Mainly:
- Clean / truncate the sessions table. This table can grow up to several millions of registers.
- Carefull with the spammers. Your comment table can grow up to similar amounts if too many spammers take a look at you. If the problem is big, simply delete with phpmyadmin:
- delete from comments where status = '1'; // unpublished comments
- delete from comments where status = '0'; // all published comments