I have a friend with a small business with a website. He asked me if he should make a put a section on his landing page under the fold that with his most recent review (or something along those lines). Specifically, he wants to know if that's the most efficient use of his time. Is there a list or such of things google values compared to each other, so that these kinds of answers could be easily answered?
Based on my own experience, I see no reason why changing part of the page periodically would have any benefit to rankings. There are other, much more important factors in how/why/where a site ranks.
Certainly, it's good to have new content added to the site regularly. But just shifting around one portion of one page doesn't present any real benefit IMO.
Some of my best ranking pages historically virtually never change.
Yes it helps
Google tracks how recently a page has been updated and distinctly favors pages that have been updated more recently (especially within the past week). I have multiple clients who consistently rank 1st-2nd in SERPs on weeks thier home page changes, and 3rd-4th place on weeks where we forget to do that. If you are in a particularly non-competitive area, then yes as the accepted answer says, it may not be necessary, but you can't compare 1 site to another when judging the effectiveness of an SEO technique, you have to compare it to itself because each site's competition is unique.
In most cases, the difference between ranking 1st and 3rd is enough to double your organic search traffic; so, unless you are actually ranking 1st without updating content, you should be updating your content (time/budget permitting).
The important part here though is to make your changes below the fold to something low priority in Google's eyes to make sure that you are not hurting your SEO with the changes. If you change something like the H1 header, then you could do more harm than good, but doing this as something in, or just above your footer works great to boost SERPs with minimal risk.