Admin Tools records every request it has blocked as suspicious in the #__admintools_log table. This information is used to determine when to block certain IP addresses based on the criteria in the Auto-ban tab of the Configure WAF page of the component. It is also used to present statistics on blocked requests in the Admin Tools' Control Panel page.
The problem is that this table can become big. Really big. Millions of records big. This makes it slower, consumes database space for no good reason and become more prone to breaking for reasons that have to do with how MySQL handles very large tables with a large volume of reads and writes.
It is strongly recommended to keep its size relatively small. How small? This depends on each site. You need to keep enough records on that table to let the Auto-Ban work correctly and possibly to display accurate statistics for the last 30 days. That's why there is no hard-coded rule on how many records to keep on that table.
This task type allows you to periodically clean up the table and keep a certain number of records. It is recommended to use a value between 1000 (one thousand) on small sites and 100000 (one hundred thousand) on larger sites. You can set that up in the Maximum blocked requests log entries option of the task.
We recommend running this task between once every two hours on very busy sites to once a week on sites with not that much traffic.