MaintenanceAny dynamic content management system needs periodic maintenance to "collect the garbage" (Wikipedia) by cleaning unnecessary data and allowing the engine to perform faster. The maintenance routine is not only used to clean the system, it's also needed to perform other tasks involving users, security systems, logs, newsletter etc.
An inefficient maintenance could lead to slow loading pages, excessive cpu and memory usage and potentially to serious problems with your server.
To avoid problems in MemHT, it should be launched at least once a day, but the number of recommended executions might be much higher for websites with high traffic load.
When the Cron daemon (Wikipedia) is not available or it's not enabled, the maintenance is executed by the engine each time someone visits the website. The continuous execution of the script is prevented by the "Core maintenance pause" interval, set in the site configuration.
This is not the best solution anyway, visitors could experience occasional slow loading pages (because the engine is performing several tasks, besides showing them the desired content).
CronThe solution is of course, Cron, know also as Crontab or Cronjobs. We recommend to set it's execution every hour, it will be enough for 99% of MemHT installations.
Don't forget to enable it in the site configuration ;)