Generally, at least part of a lot of software must be compiled. Doing this in a clean (and possibly cross-platform) way is not trivial.
However, having a somewhat standard build system makes uptake by new users and developers much easier and makes it more likely that the code will be maintained in the future. Therefore, use of common build systems is encouraged. For most compiled C/C++/Fortran code encountered in computational chemistry, CMake is recommended.