A client of JMA's was finding that when running the job.process_mailing CiviCRM job that php was ending up hitting memory limit issues. We applied a patch to have civicrm entity not trigger the pre and post hooks during cron running and that seems to at least on some testing on their staging site improved the situation. I should note that it seems like they have had the Record Activities on CiviMail deliveries enabled which might have also triggered part of the issue as rather than just mailing jobs there was Activity and ActivityContact records triggering the _pre and _post hook implementations in CiviCRM entity.
This is mostly about flagging this as a possible situation.
Active
4.0
Code
Thanks for the heads up Seamus. Would you or JMA like to create a PR in the github repo https://github.com/eileenmcnaughton/civicrm_entity for the 4.0.x branch, and we'll review and think about it.