Can someone explain the importance of this?

It’s effectively a much more coherent, powerful way to do metaprogramming at compile time than overloading the template machinery.

Just as side note that it has gotten much better since we have constexpr if and concepts, no one should be doing SFINAE and template tag dispatching by C++20 onwards.

But this naturally is even better, disregarding the lack of taste on the newly added syntax.

To paraphrase a famous committee member, "This is C++", so what else to expect in syntax proposals.