Debugging is good for finding out if a piece of code is causing problems, such as a white screen or invalid responses.
You can enable debugging by going into Configuration > General Settings and setting “PHP Debugging” to enabled.
If you are unable to login to the panel then you can set this in the database by running the following query:
UPDATE `settings` SET `value`='1' WHERE `name`='debugging'
Remember to disable debugging when your finished.