Which tables are safe to omit from sql-sync?
If you update to the latest dev version of Drush, you will find the following definition in examples/example.drushrc.php:

# $options['structure-tables']['common'] = array('cache', 'cache_*', 'history', 'search_*', 'sessions', 'watchdog');


The wildcard syntax is very useful, as with it, it is no longer necessary to make a comprehensive list of all cache tables used by all of your contrib modules.  Note that you must use the latest version of Drush pulled from git; the 8.x-6.x-dev from 18 June does not have wildcard support.