Errors, Warnings, and Log Settings
Fix Errors Whenever Possible
Although hiding error messages is important from a security perspective, errors and warnings mean that something isn't working correctly, and that could likely have a negative effect on your site. It's best to try to fix them to fix them if you can (especially if they are in your own code), or for third-party contrib modules, report them to the module or project owner.
PHP Message Types
PHP, which Drupal runs under, can generate three types of messages: