There's an extra point with notices: they are likely to lead to logical errors instead of technical ones. The algorithm works, but it receives a garbage value (

There's an extra point with notices: they are likely to lead to logical errors instead of technical ones. The algorithm works, but it receives a garbage value (null aka zero, usually). So it gives some garbage as a result. In nine cases, resulting garbage goes further into various barely meaningful code, but in one it will go into some user-facing functionality, including handling of money.