Another SEO mystery solved for me:
Follow links are links that count as points, pushing SEO link juice and boosting the page rank of the linked-to sites, helping them go higher in the SERPs as a result.
A no follow link is a link that does not count as a point in the page’s favor, does not boost PageRank, and doesn’t help a page’s placement in the SERPs.
As a webmaster, you might find yourself wondering when to use the no follow attribute and when to allow for do follow links. No follow links primarily belong in:
Paid links (it wouldn’t be fair to buy link juice, now would it?)
Anything involving what Google calls “untrusted content”