What are the performance implications of running a frequent simplenews cron task to send emails? In the Simplenews docs there is the following tip:


  The Elysia Cron module (http://drupal.org/project/elysia_cron) can be
  used to start the simplenews cron hook more often than others, so that
  newsletter are sent faster without decreasing site performance due to
  long-running cron hooks.


This is great because it will clear the mail spool without waiting for several cron runs to occur. However what are the performance implications of running this cron task on an ongoing basis with a short interval of say 30 minutes? Especially if a newsletter only gets sent once a month. i.e. My simplenews cron task in running every 30 minutes with nothing to do.
Once every 30 minutes will most likely not cause any issues. I've never used that module before so I can't saw with 100% certainty. If you where to change the frequency from 30 minutes to 1 minute I might start to worry as that could increase your server load.