When would this be useful? If your site has a blog with public commenting turned on, links within those comments could pass your reputation to pages that you may not be comfortable vouching for. Blog comment areas on pages are highly susceptible to comment spam. Nofollowing these user-added links ensures that you're not giving your page's hard-earned reputation to a spammy site.
Brian, great post as always! Question: Do you consider authority sites (industry portals) a form of “influencer marketing?” e.g. guest blogging, etc? In some niches there are not so many individuals who are influencers (outside of journalists) but there are sites that those in the industry respect. I am in the digital video space and for me one site is actually a magazine that is building a very strong digital presence. Thanks, keep up the good work!
Lastly, it's important to remember that paralysis by over-thinking is a real issue some struggle with. There's no pill for it (yet). Predicting perfection is a fool's errand. Get as close as you can within a reasonable timeframe, and prepare for future iteration. If you're traveling through your plan and determine a soft spot at any time, simply pivot. It's many hours of upfront work to get your strategy built, but it's not too hard to tweak as you go.