If linking to contextual sites is beneficial for SE rankings, what impact does the re=“nofollow” attribute have when applied to these outbound contextual links?

[danielpressley]

Communities, opinion-formers, even Google representatives, seem to offer a consensus that linking to quality, relevant sites is good practice and therefore beneficial for SEO. Does this still apply when the outbound links are "nofollow"?

Is there any good research on this out there?

[DonnaDuncan]

It's beneficial because you're helping your audience and they will appreciate and remember that. Perhaps they'll refer you to others, link to you, bookmark or share your content (getting you more exposure) or come back and visit your site another time.

Is there evidence to support that claim?

• Highlights from the 2014 Search Ranking Factors Study completed by Search Metrics and published in August/September 2014 states that "Although the off page factors were within a margin of error, it was interesting to me to find that volume of nofollow backlinks is now well correlated with higher rankings [emphasis added]. This aligns with the findings that Rand Fishkin and the IMEC Labs team of experimenters uncovered earlier in the year."
• Nicole Kohler from Moz wrote a post just this past June that shares anecdotal evidence that nofollow links have lots of "hidden" power. It's well written, logical and convincing.
• Google (via Matt Cutts) has stated repeatedly that they value "natural" link profiles without ever clearly defining exactly what that is. That said, Webmaster Tools will issue a warning if considers your link profile suspect.

Hope that helps.