If you know that the behavior is undefined, and you still require this
type of experimentation to convince yourself of something, it suggests
that you don't understand what it means for behavior to be undefined.
There's nothing of which I need convincing with respect to undefined
behavior. Anyone who relies on undefined behavior is living in sin.
However, it's a simple fact that failures happen. Failures happen
_lots_. They happen when you write code and they happen when other
people write code which is then dumped in your lap. Understanding how
your compiler acts when pushed out of spec is valuable knowledge in
debugging. Understanding what the symptoms are (or "may be", since
undefined behavior is not required to be reproducible) is a good way to
equip yourself for spotting problems in the future.
As an example, while I would certainly never want to work with a
programmer who deliberately wrote off the end of arrays, I would
certainly never want to work with a programmer who had no idea what
problems a buffer overflow could create, or the symptoms of those
problems.