What does it mean start a worker process (w3wp.exe) in debug mode?

All, According the WAS.The document says the worker process is managed by WAS .

But I found when typing w3wp /? There is a debug flag.

-debug 
   This option launches a worker process using the default 
   application host config file.  By default, it will use 
   site id 1. 

What does mean start worker process in debug mode? In what case we want to start a work process with debug option ? thanks.

Added

I didn't known why I got a exception when run w3wp.exe -debug.

ERROR: There has been an error during processing of this command. Please check the event log and see if any errors or warnings have been logged.

When I checked the log. It looks like:

The World Wide Web Publishing Service failed to set the application pool for the application '/xxxx' in site '1'. The data field contains the error number.

According to http://support.microsoft.com/kb/183480 it switches the security context of the running user which is not its normal mode of operation - I suppose this would make it easier to then attach a debugger and other utilities.