Updated packages are made available for Ubuntu quite often, sometimes even daily. These updates mainly include the latest security updates, but may also include new features. Since Ubuntu 16.04 is an LTS release, security updates are much more common than feature updates. Installing the latest updates on your server is a very important practice, but, unfortunately, it's not something that all administrators keep up on for one reason or another.
Security updates very rarely affect your server, other than helping to keep it secure against the latest threats. However, it's always possible that a security update that's intended to fix a security issue ends up breaking something else. This is rare, but I've seen it happen. When it comes to production servers, it's often difficult to keep them updated, since it may be catastrophic to your organization to introduce change within a server that's responsible for a large portion of your profits. If a server were to go...