Probably that the original binding of p is immutable, as it would be in a functional language: you can create a new binding, but you can't actually change the value of the existing binding.
x = 5;
int* p = &x;
x = 6; // new binding of x
printf("%i\n",*p);
E.g. you can turn a C program into SSA, but if you have aliasing issues, it's not gonna fix them...