Really, the only good reasons to quote a post are:
a)You are quoting only part of a post to indicate what part you are responding to
b)You break the quote into several parts, giving your comments to each part under it
c)You are quoting from a different thread
d)The post you are replying to is a few days old and/or on a different page, to help the linear mode users out.
Especially if the post being replied to is on the same page, there is no reason to quote the whole thing, because everyone can just click the "in reply to" link to jump to the post without even having to load a page.
Threaded Mode