One change in our guidelines for references sparked a discussion on Twitter, so we thought we would use this blog post to clarify and discuss. The guidance in Section 9.36 about shortened URLs is (a) optional and (b) applicable only to references that include a long or complex URL. Because shortened URLs are not guaranteed to last, they may be most appropriate for short-lived works like student papers rather than for published works.
The guidance in question reads as follows:
When a DOI or URL is long or complex, you may use shortDOIs or shortened URLs if desired. Use the shortDOI service provided by the International DOI Foundation (http://shortdoi.org/) to create shortDOIs. A work can have only one DOI and only one shortDOI; the shortDOI service will either produce a new shortDOI for a work that has never had one or retrieve an existing shortDOI.
Some websites provide their own branded shortened URLs, and independent URL shortening services are available as well. Any shortened URL is acceptable in a reference as long as you check the link to ensure that it takes you to the correct location. See Examples 4 and 18 in Chapter 10 for a shortDOI and a shortened URL, respectively, used in a reference.