OR

You're reading a file and using the details in that file to control your build.

OR

You need to loop through a set of properties and apply a specific update to each value before the build.

OR

You need to invoke complex build logic based on the platform you're building for (nested ifs).

etc.

There are lots of odd situations you end up in with real projects.

The flexibility this provides comes at the cost of build complexity though.

Obscure syntax and odd custom DSL's (>_> cmake, make, powershell) are bad because they introduce complexity and destroy the readability and maintainability of the build.

You basically need a test suite for your build code to make sure it's building correctly. Terrible.

...but, necessary. I'm not a java guy, but writing C and C++? You need to do this stuff all of the time. scons or cmake really make life a lot easier than trying to force Makefiles to do things with their obscure lambda syntax.