CLS or Cumulative Layout Shift issues occur when you’re on a web page and all of a sudden the content shifts around unexpectedly. Your users have certain expectations when they finish reading an article, checking out a link, or browsing through a list of articles, for example. The unexpected happens and the content shifts around or worse, they click on a completely different link. Pages that shift around don’t provide a good user experience.
The effect of this instability is often that the user has to refocus repeatedly to view the content on the page. Sometimes the effect of the shift is benign. All the user has to do is find their spot on the page again to continue viewing.
For example, if you are trying to get a user’s attention and have a button or link appear, and it slightly shifts down when they click, users might be frustrated and click the ad or the wrong link. They may click on the ad when they didn’t want to, and because they weren’t expecting that to happen, they might decide not to return. But as a website owner, it could turn potential clients away or, worse, turn them against you.