It is hard to remember by heart what every variable does. Even I cannot do it, and I work with them every day. One solution is to go to the list of options and exclude each of them one by one. But that’s not easy. Version 5.1 of MySQL has 291 variables, my outdated 5.5 installation has 321, and no one can guarantee that this value will not grow in the future. If you use a custom storage engine, it can have its own options as well.

It is much easier to check how the MySQL server should work with no options specified, i.e., if it uses the defaults for all values. If you have a rough guess about how mysqld should work with no custom options set, you can start the server with the --no-defaults option and compare the results to those you get when custom options are set.