(HTTP) This option tells the -O, --remote-name option to use the server-specified Content-Disposition filename instead of extracting a filename from the URL.
If the server specifies a file name and a file with that name already exists in the current working directory it will not be overwritten and an error will occur. If the server doesn't specify a file name then this option has no effect.
There's no attempt to decode %-sequences (yet) in the provided file name, so this option may provide you with rather unexpected file names.
WARNING: Exercise judicious use of this option, especially on Windows. A rogue server could send you the name of a DLL or other file that could possibly be loaded automatically by Windows or some third party software.