toKernel aim of making developer's life easier would not be met if debugging options had been left out.
All application events can be traced by defining the "log_debug" option as 1 in the application configuration file.
This option gives you a way to still get application debug information at runtime when its running in development mode, regardless of whether on screen display of errors has been enabled or not.
When developing a web aplication, you also have the option to receive debug information at the bootom of the web page.
For CLI, this debug information can be shown in the CLI output.