That is actually wrong. The -I flag set the request method to HEAD. So in some cases it will return different headers than a normal get request (and some servers don't implement HEAD responses at all).
alias h='curl -sIX GET -w "Total time: %{time_total} s\n"'
> The HEAD method is identical to GET except that the server MUST NOT return a message-body in the response.
and that
> The metainformation contained in the HTTP headers in response to a HEAD request SHOULD be identical to the information sent in response to a GET request.
curl -o/dev/null -D- http://www.example.com
-i, --include (HTTP) Include the HTTP-header in the output. The HTTP-header includes things like server-name, date of the document, HTTP-version and more...
-I, --head (HTTP/FTP/FILE) Fetch the HTTP-header only! HTTP-servers feature the command HEAD which this uses to get nothing but the header of a document. When used on an FTP or FILE file, curl displays the file size and last modification time only.