that is for when you want to do Multi Quotes.
you click the Quote button on all the posts which you wish to quote, then scroll down to the bottom of the page and click on 'Add Reply' then all the posts you clicked quote on will be in your reply form so you can reply too all of the posts at the same time rather than lots of seperate ones.
i suppose im kind of new to this site too as i signed up, then never posted for a long time and only now have i started to post a bit so hello everyone