"Silo" site structure and no-follow

What are your thoughts on the when to use no-follow on internal post, page and category links and also no-index on category landing pages?

Why would you want to do that? As a general rule, I want to give Google full access across all of my site, to ensure that it can find all the content and index it to best answer surfers’ queries.

The only exception to that would be if I had alternative formats, eg PDF versions of pages that are also available as (and linked to from) regular HTML pages - in which case, I would try to steer Google away from the PDFs and have people land at the HTML pages instead.

internal linking with dofollow is necessary for your inner pages.
in many cases long tail keywords from the inner pages generate significant amount of traffic, you really dont wanna loose them.