it should hardly ever come up, No?
Firstly, I am not a programmer. Secondly, it strikes me that you're correct in normal use.
However, somebody intent on causing trouble can pop this into a malicious program to cause havoc. It's like saying the bullet will be safe so long as it's kept in the box.
Can anyone offer a reason for using this segmented crap in any 32-bit system? If we're needing backwards compatibility for shitty old 16-bit applications, surely that can be isolated in an emulator or something these days?