Saves you filling out a citation template every time you want to cite a source. If your source has a PMID, just enter {{Cite pmid|PMID of your source}}
.
If another Wikipedia article already uses that reference (via the Cite pmid template), it will automatically use the existing information to present the full citation details of the reference in the article. If not, a bot will retrieve the information from PubMed and create the citation for you within a few minutes.
Use like this:
<ref name="Example2006">{{Cite pmid|12122621}}</ref>
To refer to the same reference elsewhere in the same article, use:
<ref name="Example2006" />
The template works by transcluding a template, which is stored as Template:cite pmid/xxxxxxxx. This subpage is filled out by a bot using the {{cite journal}} syntax. If the article already exists in, say, Template:Cite doi, a redirect to the appropriate page will be created.