what does CTFE get that external code gen dosn't?

[BCS]

If you can compile a program with CTFE then you can compile and run a D program.
If you can do that then you can run the same code and  have it generate .d 
file and then compile that on the next pass.

CTFE for data generation isn't mush harder to work with.

All I'm seeing is that CTFE lets you do it all in one pass (or with bud and 
no "fun stuff")

a script, makefile or whatever should be used for anything of any complexity 
so forgetting to do something isn't much of a problem.

So what does CTFE get you?

I'm wondering if anyone has some examples of where CTFE is a big plus over 
the other options.