If you're running the imaginary distrubution Bo-Weevil Linux 33.1 and keep up diligently with package updates, you may wonder what to do when Bo-Weevil version 33.2 is released. Is upgrading to version 33.2 a necessary part of keeping current?
Maybe, but probably not. Generally speaking, distribution upgrades (as opposed to package updates) add features, packages and yes, security fixes, but upgrading your distribution usually doesn't make your system inherently more secure. In other words, your fully patched Bo-Weevil 33.1 system is probably more secure than an unpatched Bo-Weevil 33.2 system and probably at least as secure as a patched 33.2 system.
By all means, upgrade your distribution if the new version has features that you like. Upgrade immediately if your older version is officially dropped from active support (i.e., if security updates are no longer being provided). But if neither is the case, keep updating your older distribution and try not to feel any version-envy.