Some of this is mentioned elsewhere, but just to be certain.

Use at your own risk.  This program is operated from the CLI and is only
intented to close a window that has already been killed by grim reaper (or
whatever may be equivalent under earlier versions of the OS.. I'm not 
sure there is anything).

Using it on a functioning window will usually close the window "OK",but leads
to possible disaster in other respects.  It's almost (maybe absolutely)
guaranteed that the window won't be openable from an icon again.  It may not
happen the first time, but eventually will result in the Workbench being
"killed" as well.

I wouldn't suggest using it on an AmigaShell window under any 
circumstances.

Generally, use it with caution, and only on a window killed with grim reaper.

For AmigaOS 3.9, it's only for experimentation.