Another example of arbitrary pointer comparison I'm familiar with is for resolving lock ordering problems. If I have a big set of locks that I need to take to complete a particular operation, a simple way to prevent deadlocking is to acquire those locks in the order of their pointers.

E.g. if I have three locks I need to take,

  lock_t *a = (lock_t *)0x100;
  lock_t *b = (lock_t *)0x300;
  lock_t *c = (lock_t *)0x200;

then I'll take them in order a, c, b;