Displaying WordPress version numbers makes you vulnerable to version targeted attacks. Lists of WordPress version numbers against the known vulnerability in it are readily available online. It becomes very easy for a hacker to hack you if he knows what you are vulnerable to.
If you diligently update your website, showing the version number brings no consequence for you. However, if you are using an outdated WordPress version then displaying it might not be a very prudent idea.
To learn how to hide the WordPress version number, check out this blog here.