curl --silent --show-error
The man page is trying to tell you that these options are to be used together. This means
Run curl in silent mode, and show no output unless there is an error.
S cannot be used with any other options, and
s can be used without
S. These options are most useful in shell scripting.
Example: (Pseudo Code)
do while displayInputPrompt
curl -sS http://www.example.com/path/to/some/tar/file/file.tar.bz2
In the example, notice that the user won't see any output during the data fetch. The user will only see the input prompt displayed in the displayInputPrompt function, unless there is an error, in which curl will print the error to
stdout i.e. your screen.