I turned on this mode.
Otherwise, show the white screen.
This mode is completely useless, because of it hangs up usually in some 3rd Party Plugins.
You should let it disabled, and turn on error_reporting and display_errors instead. There MUST be an fatal error.
Maybe an configuration setting uses an old absolute path
In the database could also be an absolute path, think it was modx_system_settings
We also had some Problems when an very cool Linux Administrator use rsync with an parameter to exclude all with "cache" in the filename