When should I clean up unnecessary database documents (e.g. old post or already read notifications)

Hi, I was just wondering what is the best practice for cleaning up my deployed databases. For example, I have a Notifications database, where I want to delete all notifications that have been read by the user and are at least 3 days old.

Should I check for the above conditions in a Meteor.startup function or is there a more clear way to do this server-side/automatically?

Write a job to take care of the clean up server-side, and schedule it to run regularly using percolate:synced-cron.