Logs are automaticaclly used on their purpose. Security is used by certain plugins, setup by, well, setup and debug is the general one.
Note that it only logs server (PHP) based errors, not browser related ones like JavaScript errors. For those see the log of your browser. In any case try to use an as current browser as your system allows.
Also debug log may not log all errors as some are only logged in your server's error log (yes that has one as well, ask your host where to find it).
As to the issue reported we were not able to reproduce it so far. It might be because of host limit as shared hosts often do that.