I am going to explain how I understand this. I could be wrong on some of the details because of two different reasons.... 1) I simply am wrong... or .... 2) I am correct according to what search engines have said in public but they are doing something different in practice.
When nofollow was first introduced a lot of people used it to "sculpt" the flow of pagerank. They were told at that time by some search engine employees that pagerank did not flow into nofollowed pages. That is how search engines who made public statements about it were supposed to be treating it in the beginning.
Later we learned that google (and maybe other) search engines changed their mind on how they handle nofollow and that change was to evaporate ALL pagerank that would have flowed into a nofollow link. In that situation it would be a bad idea to use nofollow because the pagerank was permanently lost.
Do they still handle nofollow links that way? I don't know.
However...... how I currently understand it is that if you designate a page as noindex / follow then pagerank flows into that page and through the links on that page. This would conserve any pass-through pagerank but would result in a loss of any pagerank that is retained in that page (or maybe it all passes through since the page is no index - I don't know).
So, if I had pages that I wanted to link to on my site but didn't want in the index I would use noindex / follow to allow the pagerank that flows into those pages to pass through to other pages on my site. But I would never be sure that it really works that way. Also, keep in mind that there are numerous search engines and there could be many different ways of treating these links - and pagerank is a substance unique to google.
If anyone understands this differently or suspect that it does not work as explained, please let us know.