What's the point of unnamed non-type template parameters?

Question

According to the reference, the name of a non-type template parameter is optional, even when assigning a default value (see (1) and (2)). Therefore these template structs ar

Answer 1

What's the point of unnamed/anonymous non-type template parameters?

I can think of specialization:

template
struct Foo{
   char x;
};

template<>
struct Foo<0> {
   int x;
};

template<>
struct Foo<1> {
   long x;
};

Then:

Foo<0> a; // x data member is int
Foo<1> b; // x data member is long
Foo<7> c; // x data member is char
Foo<>  d; // x data member is char