The answer depends almost entirely upon which software sources you have enabled in your Software & Updates control panel.
If you stick to the official Ubuntu repositories, you usually will get safe, signed, tested updates that you can install worry-free. Perhaps once or twice a decade one of these update may cause a problem, so regular backups are still wise.
Caveat: Do NOT enable the Ubuntu -proposed repository unless you are helping to test the proposed software. Those will sometimes cause problems. That's what testing is: Discovering the problems.
If you have added a lot of non-Ubuntu sources (like third-party sources and certain PPAs), then the risk of a crash, conflict, or other problem goes up substantially.