nofollow is the property telling search engines not to pass the link juice to the linked page.
For example <a href="x.htm" rel="nofollow">click</a> is there in a page y.htm.
Now when the search engines look for nofollow property they will not pass the link juice(i.e. weightage to the page x.htm from the page y.htm).
nofollow does not benefit seo work.