The resources here are amplified elsewhere.

As a specific example, expanding constexpr means a codebase I recently worked on can move away from template metaprogramming magic to something that is more idiomatic. That means iterating on that code will be easier, faster, and less error-prone. I've already done static dispatch using constexpr and type traits that would have taken longer to do with templates.

Currently constexpr programming needs you to know the specifics of what is supported - ideally you'll be able to infer that from first principles of the invariants that are available at compile time. That leads to faster, more confident development.

It's a similar story for reflection: we were using custom scripts and soon won't have to. The changes usually come out of the problems people are already finding solutions for in the real world, rather than gilding a lily.