Evolution, Security, and may be more.

But you must update a clone site in order to check for bugs

Sometimes a plugin is not updated or we have conflicts that create problems like white screen, so be carefull.

And always backup before and after the update.google says

With each new release, they fix bugs, add new features, improve performance, and enhance existing features to stay up to date with new industry standards. So in other words, when you do not update your WordPress site, you are risking your website security and missing out on new features / improvements

Do not update. Wait to see what happens when other people update for few months and then decide.