The compile time execution itself is just one piece of the puzzle, the other two being compile time reflection (which I think is actually the key piece) and the built in code generation.

Running functions alone is not that interesting, and neither really is generating code. You can do those (arguably better for some cases) with helper programs as a separate build step. But reflection is non-trivial to do externally, so that's the biggest value add, and using it with all three pieces let you close the loop.