This is yet another article that goes on and on about nonsensical situations that are just shitty code.
Who cares?
The short flippant answer is: because everyone writes shitty code at some point. It generally doesn't get committed or released, but during development, shitty buggy code with Undefined Behavior happens.
Here's a concrete example of some code that I actually wrote (simplified greatly so it could be a small illustrative example): https://godbolt.org/z/xzehrWE57
Knowing about UB is a useful way to describe what's going on in this code example, and why the compiler is doing what it's doing. If you see your code behaving in "impossible" ways, knowing about UB can give you some hints about where to look.
Comments
The short flippant answer is: because everyone writes shitty code at some point. It generally doesn't get committed or released, but during development, shitty buggy code with Undefined Behavior happens.
Here's a concrete example of some code that I actually wrote (simplified greatly so it could be a small illustrative example): https://godbolt.org/z/xzehrWE57
Knowing about UB is a useful way to describe what's going on in this code example, and why the compiler is doing what it's doing. If you see your code behaving in "impossible" ways, knowing about UB can give you some hints about where to look.