When choose Julia
As we priviously mentioned, Julia is not magic and there is no silver bullet, we have to choose our language for certain problems, here are some suggestions:
When you need Julia
if you usually need to optimize Python with C/C++/Fortran/etc.
if your program reqiures a lot loops and matrix multiplications and other computation heavy tasks
if your problem requires a lot abstractions but also sensitive to performance.
if your interface will looks better with a DSL, or some addons on its original language. (like einsum for tensor contraction)
Your collaborator or supervisor use Julia.
When you don't need Julia
Your program is heavily based on pure Python and its packages (like Pytorch, MXNet, TensorFlow, etc.), and there is no better or equivalent Julia packages.
You care about performance, but most of your functions and commands will only be executed few times. (because we have a JIT overhead in Julia)
You don't care performance very much at the moment, about 5x slower is acceptable. (tasks like GUI, plotting, etc.)
Your collaborator or supervisor do not accept new language.