Use noindex and nofollow if you want to completely prevent Google from indexing certain pages as well as any pages linking to them. This is usually for the hidden section of your site that you do not want it to appear on the search result pages.
Also use noindex and dofollow if you want to prevent duplication on your own website, especially URLs which contain parameters. For example, to avoid Google from indexing this URL http://abc(dot)com/pages=1?search=keyword%null&location=new%20york&data=offline which is the same as http://abc(dot)com/.
Index but nofollow, this is only usually for pages where you want the search engines to index but do not want it to follow the links within that page. Usually these links will go to external sources such as other website that is why you have to put nofollow to prevent the leakage of link juice.