Well, you can use this to write compile time code like this:
#include <iostream>template <int N> const int ctSquare = N*N;int main() { std::cout << ctSquare<7> << std::endl;}This is a significant improvement over the equivalent
#include <iostream>template <int N> struct ctSquare { static const int value = N*N;};int main() { std::cout << ctSquare<7>::value << std::endl;}that people used to write to perform template metaprogramming before variable templates were introduced. For non-type values, we were able to do this since C++11 with constexpr, so template variables have only the advantage of allowing computations based on types to the variable templates.
TL;DR: They don't allow us to do anything we couldn't do before, but they make template metaprogramming less of a PITA.