What is the difference between using partial and not using partial for tornado.options.define?

I see two ways of setting up define in tornado.

import tornado.options
def define_web(hidden=False):

    define = partial(tornado.options.define, group='Web', hidden=hidden)
    define('thread', False, type=bool,
        help='threading')

and without using partial

from tornado.options import options, define

def define_web(hidden=False):
    define('thread', False, type=bool,
        help='threading')

So I was wondering what is the difference, and what is advantage of using partials