Nobody I know is doing this, and I don't know why.
Some people do it, but it's called differently than what you said: it's "taking a gap year." During a gap year, you are not affiliated with academia, and (depending on your field), you could consider either working in industry, or working on some side projects. This can be the right decision for some people, particularly if you are burned out from your PhD and need a break. In terms of your career, it has some possible downsides, though, most importantly that (i) you may be unpaid and (ii) your research will likely lose momentum. If you are potentially interested in an academic career, the lost momentum can be damaging. At the postdoc stage in many disciplines the goal is to keep papers always "in the pipeline" while new projects are being started, and a gap year can unfortunately disrupt this flow.
It may be possible to join a postdoc mid-year, in which case the gap year would become a gap-half-year, but as the normal cycle is to join in the fall I would not count on this necessarily working out.
If the above description of a gap year doesn't fit you, there are some possible alternatives:
Stay an extra year for your PhD. If you are very happy in your PhD research and feel it is going well and you just want to continue it for another year to improve your CV before applying for postdocs, this can be a good option. However, it is not a good option if you want to graduate soon and move on do a different position.
Apply to postdocs this year, and only next year as a backup. This is another strategy I have seen which definitely fits your situation: the thought is, why not give it a shot? If you don't get in where you like, you can then reevaluate. The only potential downside is if you make a bad impression on any labs you want to join, but assuming your CV is fine and just not quite as stellar enough as you hope, I wouldn't be overly concerned about that.