I routinely used to compile C programs on other compilers to find defects that one or another didn't find. Compiling on Windows vs Linux. You could summarize / minimize it down to compiling it with warning as errors etc but you'd be missing the point.

The point wasn't actual cross-platform portability even though that was a nice side effect. It was to flush out all the weird edge cases.

Edges like security flaws. Buffer overflows are usually platform specific. There are plenty of other ways to find these issues but simply recompiling for a different platform surfaces all sorts of issues.