If your site supports paid links, you need to use nofollow in order to keep these links from giving credit to other sites. Also, if your site has a comment section that you don’t always monitor, using nofollow links prevents commenters from getting credit from you, as well as posting bad links that could hurt your SERP rankings. This also applies to content posts that other people may contribute on your business blog.
Nofollow is also helpful when embedding media (such as infographics) or widgets that you obtained from other sites. The thing is, you don’t want Google to think that you’re endorsing those sources, so you need to make sure credit is not passed on to them.
Obviously, you also wouldn’t want to boost the authority of your competitors, so you need to make sure you attach a nofollow tag when linking to a site that most probably belongs in the same industry as yours.